SLIB

1. The Library System

1.1 Feature

SLIB denotes features by symbols. SLIB maintains a list of features supported by a Scheme session. The set of features provided by a session may change during that session. Some features are properties of the Scheme implementation being used. The following intrinsic features detail what sort of numbers are available from an implementation:

• 'inexact
• 'rational
• 'real
• 'complex
• 'bignum

SLIB initialization (in `require.scm') tests and provides any of these numeric features which are appropriate.

Other features correspond to the presence of packages of Scheme procedures or syntax (macros).

Function: provided? feature

Returns #t if feature is present in the current Scheme session; otherwise #f. More specifically, provided? returns #t if the symbol feature is the software-type or if feature has been provided by a module already loaded; and #f otherwise.

In some implementations provided? tests whether a module has been required by any module or in any thread; other implementations will have provided? reflect only the modules required by that particular session or thread.

To work portably in both scenarios, use provided? only to test whether intrinsic properties (like those above) are present.

The feature argument can also be an expression calling and, or, and not of features. The boolean result of the logical question asked by feature is returned.

The generalization of provided? for arbitrary features and catalog is feature-eval:

Function: feature-eval expression provided?

Evaluates and, or, and not forms in expression, using the values returned by calling provided? on the leaf symbols. feature-eval returns the boolean result of the logical combinations.

Procedure: provide feature

Informs SLIB that feature is supported in this session.

(provided? 'foo)    ⇒ #f
(provide 'foo)
(provided? 'foo)    ⇒ #t

1.2 Require

SLIB creates and maintains a catalog mapping features to locations of files introducing procedures and syntax denoted by those features.

Variable: *catalog*

Is an association list of features (symbols) and pathnames which will supply those features. The pathname can be either a string or a pair. If pathname is a pair then the first element should be a macro feature symbol, source, compiled, or one of the other cases described in Library Catalogs. The cdr of the pathname should be either a string or a list.

At the beginning of each section of this manual, there is a line like (require 'feature). The Scheme files comprising SLIB are cataloged so that these feature names map to the corresponding files.

SLIB provides a form, require, which loads the files providing the requested feature.

Procedure: require feature

• If (provided? feature) is true, then require just returns.
• Otherwise, if feature is found in the catalog, then the corresponding files will be loaded and (provided? feature) will henceforth return #t. That feature is thereafter provided.
• Otherwise (feature not found in the catalog), an error is signaled.

There is a related form require-if, used primarily for enabling compilers to statically include modules which would be dynamically loaded by interpreters.

Procedure: require-if condition feature

Requires feature if condition is true.

The random module uses require-if to flag object->string as a (dynamic) required module.

(require 'byte)
(require 'logical)
(require-if 'compiling 'object->string)

The batch module uses require-if to flag posix-time as a module to load if the implementation supports large precision exact integers.

(require-if '(and bignum compiling) 'posix-time)

The commutative-ring module uses require-if to ensure that it has an exponentiation routine, regardless of whether the implementation supports inexact numbers:

(require-if '(not inexact) 'logical)    ;for integer-expt
(define number^ (if (provided? 'inexact) expt integer-expt))

The catalog can also be queried using slib:in-catalog?.

Function: slib:in-catalog? feature

Returns a CDR of the catalog entry if one was found for the symbol feature in the alist *catalog* (and transitively through any symbol aliases encountered). Otherwise, returns #f. The format of catalog entries is explained in Library Catalogs.

1.3 Library Catalogs

Catalog files consist of one or more association lists. In the circumstance where a feature symbol appears in more than one list, the latter list's association is retrieved. Here are the supported formats for elements of catalog lists:

(feature . <symbol>)

Redirects to the feature named <symbol>.

(feature . "<path>")

Loads file <path>.

(feature source "<path>")

slib:loads the Scheme source file <path>.

(feature compiled "<path>" …)

slib:load-compileds the files <path> ….

(feature aggregate <symbol> …)

slib:requires the features <symbol> ….

The various macro styles first require the named macro package, then just load <path> or load-and-macro-expand <path> as appropriate for the implementation.

(feature defmacro "<path>")

defmacro:loads the Scheme source file <path>.

(feature macro-by-example "<path>")

defmacro:loads the Scheme source file <path>.

(feature macro "<path>")

macro:loads the Scheme source file <path>.

(feature macros-that-work "<path>")

macro:loads the Scheme source file <path>.

(feature syntax-case "<path>")

macro:loads the Scheme source file <path>.

(feature syntactic-closures "<path>")

macro:loads the Scheme source file <path>.

1.4 Catalog Creation

At the start of an interactive session no catalog is present, but is created with the first catalog inquiry (such as (require 'random)). Several sources of catalog information are combined to produce the catalog:

• standard SLIB packages.
• additional packages of interest to this site.
• packages specifically for the variety of Scheme which this session is running.
• packages this user wants to always have available. This catalog is the file `homecat' in the user's HOME directory.
• packages germane to working in this (current working) directory. This catalog is the file `usercat' in the directory to which it applies. One would typically cd to this directory before starting the Scheme session.
• packages which are part of an application program.

SLIB combines the catalog information which doesn't vary per user into the file `slibcat' in the implementation-vicinity. Therefore `slibcat' needs change only when new software is installed or compiled. Because the actual pathnames of files can differ from installation to installation, SLIB builds a separate catalog for each implementation it is used with.

The definition of *SLIB-VERSION* in SLIB file `require.scm' is checked against the catalog association of *SLIB-VERSION* to ascertain when versions have changed. It is a reasonable practice to change the definition of *SLIB-VERSION* whenever the library is changed. If multiple implementations of Scheme use SLIB, remember that recompiling one `slibcat' will update only that implementation's catalog.

The compilation scripts of Scheme implementations which work with SLIB can automatically trigger catalog compilation by deleting `slibcat' or by invoking require of a special feature:

Procedure: require 'new-catalog

This will load `mklibcat', which compiles and writes a new `slibcat'.

Another special feature of require erases SLIB's catalog, forcing it to be reloaded the next time the catalog is queried.

Procedure: require #f

Removes SLIB's catalog information. This should be done before saving an executable image so that, when restored, its catalog will be loaded afresh.

1.5 Catalog Vicinities

Each file in the table below is descibed in terms of its file-system independent vicinity (see section Vicinity). The entries of a catalog in the table override those of catalogs above it in the table.

implementation-vicinity `slibcat'

This file contains the associations for the packages comprising SLIB, the `implcat' and the `sitecat's. The associations in the other catalogs override those of the standard catalog.

library-vicinity `mklibcat.scm'

creates `slibcat'.

library-vicinity `sitecat'

This file contains the associations specific to an SLIB installation.

implementation-vicinity `implcat'

This file contains the associations specific to an implementation of Scheme. Different implementations of Scheme should have different implementation-vicinity.

implementation-vicinity `mkimpcat.scm'

if present, creates `implcat'.

implementation-vicinity `sitecat'

This file contains the associations specific to a Scheme implementation installation.

home-vicinity `homecat'

This file contains the associations specific to an SLIB user.

user-vicinity `usercat'

This file contains associations affecting only those sessions whose working directory is user-vicinity.

Here is an example of a `usercat' catalog. A program in this directory can invoke the `run' feature with (require 'run).

;;; "usercat": SLIB catalog additions for SIMSYNCH.     -*-scheme-*-
(
 (simsynch      . "../synch/simsynch.scm")
 (run           . "../synch/run.scm")
 (schlep        . "schlep.scm")
)

Copying `usercat' to many directories is inconvenient. Application programs which aren't always run in specially prepared directories can nonetheless register their features during initialization.

Procedure: catalog:read vicinity catalog

Reads file named by string catalog in vicinity, resolving all paths relative to vicinity, and adds those feature associations to *catalog*.

catalog:read would typically be used by an application program having dynamically loadable modules. For instance, to register factoring and other modules in *catalog*, JACAL does:

(catalog:read (program-vicinity) "jacalcat")

For an application program there are three appropriate venues for registering its catalog associations:

• in a `usercat' file in the directory where the program runs; or
• in an `implcat' file in the implementation-vicinity; or
• in an application program directory; loaded by calling catalog:read.

1.6 Compiling Scheme

To use Scheme compilers effectively with SLIB the compiler needs to know which SLIB modules are to be compiled and which symbols are exported from those modules.

The procedures in this section automate the extraction of this information from SLIB modules. They are guaranteed to work on SLIB modules; to use them on other sources, those sources should follow SLIB conventions.

1.6.1 Module Conventions

• All the top-level require commands have one quoted argument and are positioned before other Scheme definitions and expressions in the file.
• Any conditionally required SLIB modules (1) also appear at the beginning of their files conditioned on the feature compiling using require-if (see section require-if).

  (require 'logical) (require 'multiarg/and-) (require-if 'compiling 'sort) (require-if 'compiling 'ciexyz)

• Schmooz-style comments preceding a definition, identify that definition as an exported identifier (see section Schmooz). For non-schmooz files, putting `;@' at the beginning of the line immediately preceding the definition (define, define-syntax, or defmacro) suffices.

  ;@ (define (make-vicinity <pathname>) <pathname>)

• Syntax (macro) definitions are grouped at the end of a module file.
• Modules defining macros do not invoke those macros. SLIB macro implementations are exempt from this rule.

  An example of how to expand macro invocations is:

  (require 'macros-that-work) (require 'yasos) (require 'pprint-file) (pprint-filter-file "collect.scm" macwork:expand)

1.6.2 Module Manifests

(require 'manifest)

In some of these examples, slib:catalog is the SLIB part of the catalog; it is free of compiled and implementation-specific entries. It would be defined by:

(define slib:catalog (cdr (member (assq 'null *catalog*) *catalog*)))

Function: file->requires file provided? catalog

Returns a list of the features required by file assuming the predicate provided? and association-list catalog.

(define (provided+? . features)
  (lambda (feature)
    (or (memq feature features) (provided? feature))))

(file->requires "obj2str.scm" (provided+? 'compiling) '())
        ⇒ (string-port generic-write)

(file->requires "obj2str.scm" provided? '())
        ⇒ (string-port)

Function: feature->requires feature provided? catalog

Returns a list of the features required by feature assuming the predicate provided? and association-list catalog.

(feature->requires 'batch (provided+? 'compiling) *catalog*)
        ⇒ (tree line-i/o databases parameters string-port
                   pretty-print common-list-functions posix-time)

(feature->requires 'batch provided? *catalog*)
        ⇒ (tree line-i/o databases parameters string-port
                   pretty-print common-list-functions)

(feature->requires 'batch provided? '((batch . "batch")))
        ⇒ (tree line-i/o databases parameters string-port
                   pretty-print common-list-functions)

Function: file->loads file

Returns a list of strings naming existing files loaded (load slib:load slib:load-source macro:load defmacro:load syncase:load synclo:load macwork:load) by file or any of the files it loads.

(file->loads (in-vicinity (library-vicinity) "scainit.scm"))
        ⇒ ("/usr/share/slib/scaexpp.scm"
            "/usr/share/slib/scaglob.scm"
            "/usr/share/slib/scaoutp.scm")

Function: load->path exp

Given a (load '<expr>), where <expr> is a string or vicinity stuff), (load->path <expr>) figures a path to the file. load->path returns that path if it names an existing file; otherwise #f.

(load->path '(in-vicinity (library-vicinity) "mklibcat"))
        ⇒ "/usr/share/slib/mklibcat.scm"

Function: file->definitions file

Returns a list of the identifier symbols defined by SLIB (or SLIB-style) file file.

(file->definitions "random.scm")
        ⇒ (*random-state* make-random-state
           seed->random-state copy-random-state random
           random:chunk)

Function: file->exports file

Returns a list of the identifier symbols exported (advertised) by SLIB (or SLIB-style) file file.

(file->exports "random.scm")
        ⇒ (make-random-state seed->random-state
            copy-random-state random)

(file->exports "randinex.scm")
        ⇒ (random:solid-sphere! random:hollow-sphere!
            random:normal-vector! random:normal
            random:exp random:uniform)

Function: feature->export-alist feature catalog

Returns a list of lists; each sublist holding the name of the file implementing feature, and the identifier symbols exported (advertised) by SLIB (or SLIB-style) feature feature, in catalog.

Function: feature->exports feature catalog

Returns a list of all exports of feature.

In the case of aggregate features, more than one file may have export lists to report:

(feature->export-alist 'r5rs slib:catalog))
        ⇒ (("/usr/share/slib/values.scm"
             call-with-values values)
            ("/usr/share/slib/mbe.scm"
             define-syntax macro:expand
             macro:load macro:eval)
            ("/usr/share/slib/eval.scm"
             eval scheme-report-environment
             null-environment interaction-environment))

(feature->export-alist 'stdio *catalog*)
        ⇒ (("/usr/share/slib/scanf.scm"
             fscanf sscanf scanf scanf-read-list)
            ("/usr/share/slib/printf.scm"
             sprintf printf fprintf)
            ("/usr/share/slib/stdio.scm"
             stderr stdout stdin))

(feature->exports 'stdio slib:catalog)
        ⇒ (fscanf sscanf scanf scanf-read-list
             sprintf printf fprintf stderr stdout stdin)

1.6.3 Module Semantics

For the purpose of compiling Scheme code, each top-level require makes the identifiers exported by its feature's module defined (or defmacroed or defined-syntaxed) within the file (being compiled) headed with those requires.

Top-level occurrences of require-if make defined the exports from the module named by the second argument if the feature-expression first argument is true in the target environment. The target feature compiling should be provided during this phase of compilation.

Non-top-level SLIB occurences of require and require-if of quoted features can be ignored by compilers. The SLIB modules will all have top-level constructs for those features.

Note that aggregate catalog entries import more than one module. Implementations of require may or may not be transitive; code which uses module exports without requiring the providing module is in error.

In the SLIB modules modular, batch, hash, common-lisp-time, commutative-ring, charplot, logical, common-list-functions, coerce and break there is code conditional on features being provided?. Most are testing for the presence of features which are intrinsic to implementations (inexacts, bignums, ...).

In all cases these provided? tests can be evaluated at compile-time using feature-eval (see section feature-eval). The simplest way to compile these constructs may be to treat provided? as a macro.

1.6.4 Top-level Variable References

(require 'top-refs)

These procedures complement those in Module Manifests by finding the top-level variable references in Scheme source code. They work by traversing expressions and definitions, keeping track of bindings encountered. It is certainly possible to foil these functions, but they return useful information about SLIB source code.

Function: top-refs obj

Returns a list of the top-level variables referenced by the Scheme expression obj.

Function: top-refs<-file filename

filename should be a string naming an existing file containing Scheme source code. top-refs<-file returns a list of the top-level variable references made by expressions in the file named by filename.

Code in modules which filename requires is not traversed. Code in files loaded from top-level is traversed if the expression argument to load, slib:load, slib:load-source, macro:load, defmacro:load, synclo:load, syncase:load, or macwork:load is a literal string constant or composed of combinations of vicinity functions and string literal constants; and the resulting file exists (possibly with ".scm" appended).

The following function parses an Info Index. (2)

Function: exports<-info-index file n …

n … must be an increasing series of positive integers. exports<-info-index returns a list of all the identifiers appearing in the nth … (info) indexes of file. The identifiers have the case that the implementation's read uses for symbols. Identifiers containing spaces (eg. close-base on base-table) are not included.

Each info index is headed by a `* Menu:' line. To list the symbols in the first and third info indexes do:

(exports<-info-index "slib.info" 1 3)

1.6.5 Module Analysis

(require 'vet)

Function: vet-slib

Using the procedures in the top-refs and manifest modules, vet-slib analyzes each SLIB module, reporting about any procedure or macro defined whether it is:

orphaned

defined, not called, not exported;

missing

called, not defined, and not exported by its required modules;

undocumented-export

Exported by module, but no index entry in `slib.info';

And for the library as a whole:

documented-unexport

Index entry in `slib.info', but no module exports it.

This straightforward analysis caught three full days worth of never-executed branches, transitive require assumptions, spelling errors, undocumented procedures, missing procedures, and cyclic dependencies in SLIB.

2. Universal SLIB Procedures

The procedures described in these sections are supported by all implementations as part of the `*.init' files or by `require.scm'.

2.1 Vicinity

A vicinity is a descriptor for a place in the file system. Vicinities hide from the programmer the concepts of host, volume, directory, and version. Vicinities express only the concept of a file environment where a file name can be resolved to a file in a system independent manner. Vicinities can even be used on flat file systems (which have no directory structure) by having the vicinity express constraints on the file name. On most systems a vicinity would be a string. All of these procedures are file system dependent.

These procedures are provided by all implementations.

Function: make-vicinity dirpath

Returns dirpath as a vicinity for use as first argument to in-vicinity.

Function: pathname->vicinity path

Returns the vicinity containing path.

(pathname->vicinity "/usr/share/scm/Link.scm") ⇒ "/usr/share/scm/"

Function: program-vicinity

Returns the vicinity of the currently loading Scheme code. For an interpreter this would be the directory containing source code. For a compiled system (with multiple files) this would be the directory where the object or executable files are. If no file is currently loading it the result is undefined. Warning: program-vicinity can return incorrect values if your program escapes back into a load.

Function: library-vicinity

Returns the vicinity of the shared Scheme library.

Function: implementation-vicinity

Returns the vicinity of the underlying Scheme implementation. This vicinity will likely contain startup code and messages and a compiler.

Function: user-vicinity

Returns the vicinity of the current directory of the user. On most systems this is `""' (the empty string).

Function: home-vicinity

Returns the vicinity of the user's HOME directory, the directory which typically contains files which customize a computer environment for a user. If scheme is running without a user (eg. a daemon) or if this concept is meaningless for the platform, then home-vicinity returns #f.

Function: vicinity:suffix? chr

Returns the `#t' if chr is a vicinity suffix character; and #f otherwise. Typical vicinity suffixes are `/', `:', and `\',

Function: in-vicinity vicinity filename

Returns a filename suitable for use by slib:load, slib:load-source, slib:load-compiled, open-input-file, open-output-file, etc. The returned filename is filename in vicinity. in-vicinity should allow filename to override vicinity when filename is an absolute pathname and vicinity is equal to the value of (user-vicinity). The behavior of in-vicinity when filename is absolute and vicinity is not equal to the value of (user-vicinity) is unspecified. For most systems in-vicinity can be string-append.

Function: sub-vicinity vicinity name

Returns the vicinity of vicinity restricted to name. This is used for large systems where names of files in subsystems could conflict. On systems with directory structure sub-vicinity will return a pathname of the subdirectory name of vicinity.

2.2 Configuration

These constants and procedures describe characteristics of the Scheme and underlying operating system. They are provided by all implementations.

Constant: char-code-limit

An integer 1 larger that the largest value which can be returned by char->integer.

Constant: most-positive-fixnum

In implementations which support integers of practically unlimited size, most-positive-fixnum is a large exact integer within the range of exact integers that may result from computing the length of a list, vector, or string.

In implementations which do not support integers of practically unlimited size, most-positive-fixnum is the largest exact integer that may result from computing the length of a list, vector, or string.

Constant: slib:tab

The tab character.

Constant: slib:form-feed

The form-feed character.

Function: software-type

Returns a symbol denoting the generic operating system type. For instance, unix, vms, macos, amiga, or ms-dos.

Function: slib:report-version

Displays the versions of SLIB and the underlying Scheme implementation and the name of the operating system. An unspecified value is returned.

(slib:report-version) ⇒ slib "3a1" on scm "5b1" on unix

Function: slib:report

Displays the information of (slib:report-version) followed by almost all the information neccessary for submitting a problem report. An unspecified value is returned.

Function: slib:report #t

provides a more verbose listing.

Function: slib:report filename

Writes the report to file `filename'.

(slib:report) ⇒ slib "3a1" on scm "5b1" on unix (implementation-vicinity) is "/usr/share/scm/" (library-vicinity) is "/usr/share/slib/" (scheme-file-suffix) is ".scm" loaded *features* : trace alist qp sort common-list-functions macro values getopt compiled implementation *features* : bignum complex real rational inexact vicinity ed getenv tmpnam abort transcript with-file ieee-p1178 r4rs rev4-optional-procedures hash object-hash delay eval dynamic-wind multiarg-apply multiarg/and- logical defmacro string-port source current-time record rev3-procedures rev2-procedures sun-dl string-case array dump char-ready? full-continuation system implementation *catalog* : (i/o-extensions compiled "/usr/share/scm/ioext.so") ...

2.3 Input/Output

These procedures are provided by all implementations.

Function: file-exists? filename

Returns #t if the specified file exists. Otherwise, returns #f. If the underlying implementation does not support this feature then #f is always returned.

Function: delete-file filename

Deletes the file specified by filename. If filename can not be deleted, #f is returned. Otherwise, #t is returned.

Function: open-file filename modes

filename should be a string naming a file. open-file returns a port depending on the symbol modes:

r

an input port capable of delivering characters from the file.

rb

a binary input port capable of delivering characters from the file.

w

an output port capable of writing characters to a new file by that name.

wb

a binary output port capable of writing characters to a new file by that name.

If an implementation does not distinguish between binary and non-binary files, then it must treat rb as r and wb as w.

If the file cannot be opened, either #f is returned or an error is signalled. For output, if a file with the given name already exists, the effect is unspecified.

Function: port? obj

Returns #t if obj is an input or output port, otherwise returns #f.

Procedure: close-port port

Closes the file associated with port, rendering the port incapable of delivering or accepting characters.

close-file has no effect if the file has already been closed. The value returned is unspecified.

Function: call-with-open-ports proc ports …

Function: call-with-open-ports ports … proc

Proc should be a procedure that accepts as many arguments as there are ports passed to call-with-open-ports. call-with-open-ports calls proc with ports …. If proc returns, then the ports are closed automatically and the value yielded by the proc is returned. If proc does not return, then the ports will not be closed automatically unless it is possible to prove that the ports will never again be used for a read or write operation.

Function: tmpnam

Returns a pathname for a file which will likely not be used by any other process. Successive calls to (tmpnam) will return different pathnames.

Function: current-error-port

Returns the current port to which diagnostic and error output is directed.

Procedure: force-output

Procedure: force-output port

Forces any pending output on port to be delivered to the output device and returns an unspecified value. The port argument may be omitted, in which case it defaults to the value returned by (current-output-port).

Function: output-port-width

Function: output-port-width port

Returns the width of port, which defaults to (current-output-port) if absent. If the width cannot be determined 79 is returned.

Function: output-port-height

Function: output-port-height port

Returns the height of port, which defaults to (current-output-port) if absent. If the height cannot be determined 24 is returned.

2.4 System

These procedures are provided by all implementations.

Procedure: slib:load-source name

Loads a file of Scheme source code from name with the default filename extension used in SLIB. For instance if the filename extension used in SLIB is `.scm' then (slib:load-source "foo") will load from file `foo.scm'.

Procedure: slib:load-compiled name

On implementations which support separtely loadable compiled modules, loads a file of compiled code from name with the implementation's filename extension for compiled code appended.

Procedure: slib:load name

Loads a file of Scheme source or compiled code from name with the appropriate suffixes appended. If both source and compiled code are present with the appropriate names then the implementation will load just one. It is up to the implementation to choose which one will be loaded.

If an implementation does not support compiled code then slib:load will be identical to slib:load-source.

Procedure: slib:eval obj

eval returns the value of obj evaluated in the current top level environment. Eval provides a more general evaluation facility.

Procedure: slib:eval-load filename eval

filename should be a string. If filename names an existing file, the Scheme source code expressions and definitions are read from the file and eval called with them sequentially. The slib:eval-load procedure does not affect the values returned by current-input-port and current-output-port.

Procedure: slib:warn arg1 arg2 …

Outputs a warning message containing the arguments.

Procedure: slib:error arg1 arg2 …

Outputs an error message containing the arguments, aborts evaluation of the current form and responds in a system dependent way to the error. Typical responses are to abort the program or to enter a read-eval-print loop.

Procedure: slib:exit n

Procedure: slib:exit

Exits from the Scheme session returning status n to the system. If n is omitted or #t, a success status is returned to the system (if possible). If n is #f a failure is returned to the system (if possible). If n is an integer, then n is returned to the system (if possible). If the Scheme session cannot exit an unspecified value is returned from slib:exit.

Function: browse-url url

Web browsers have become so ubiquitous that programming languagues should support a uniform interface to them.

If a `netscape' browser is running, browse-url causes the browser to display the page specified by string url and returns #t.

If the browser is not running, browse-url starts a browser displaying the argument url. If the browser starts as a background job, browse-url returns #t immediately; if the browser starts as a foreground job, then browse-url returns #t when the browser exits; otherwise it returns #f.

2.5 Miscellany

These procedures are provided by all implementations.

Function: identity x

identity returns its argument.

Example:

(identity 3) ⇒ 3 (identity '(foo bar)) ⇒ (foo bar) (map identity lst) ≡ (copy-list lst)

2.5.1 Mutual Exclusion

An exchanger is a procedure of one argument regulating mutually exclusive access to a resource. When a exchanger is called, its current content is returned, while being replaced by its argument in an atomic operation.

Function: make-exchanger obj

Returns a new exchanger with the argument obj as its initial content.

(define queue (make-exchanger (list a)))

A queue implemented as an exchanger holding a list can be protected from reentrant execution thus:

(define (pop queue) (let ((lst #f)) (dynamic-wind (lambda () (set! lst (queue #f))) (lambda () (and lst (not (null? lst)) (let ((ret (car lst))) (set! lst (cdr lst)) ret))) (lambda () (and lst (queue lst)))))) (pop queue) ⇒ a (pop queue) ⇒ #f

2.5.2 Legacy

The following procedures were present in Scheme until R4RS (see (r4rs)Notes section `Language changes' in Revised(4) Scheme). They are provided by all SLIB implementations.

Constant: t

Derfined as #t.

Constant: nil

Defined as #f.

Function: last-pair l

Returns the last pair in the list l. Example:

(last-pair (cons 1 2)) ⇒ (1 . 2) (last-pair '(1 2)) ⇒ (2) ≡ (cons 2 '())

3. Scheme Syntax Extension Packages

Syntax extensions (macros) included with SLIB.

3.1 Defmacro

Defmacros are supported by all implementations.

Function: gentemp

Returns a new (interned) symbol each time it is called. The symbol names are implementation-dependent

(gentemp) ⇒ scm:G0 (gentemp) ⇒ scm:G1

Function: defmacro:eval e

Returns the slib:eval of expanding all defmacros in scheme expression e.

Function: defmacro:load filename

filename should be a string. If filename names an existing file, the defmacro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially. These source code expressions and definitions may contain defmacro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

Function: defmacro? sym

Returns #t if sym has been defined by defmacro, #f otherwise.

Function: macroexpand-1 form

Function: macroexpand form

If form is a macro call, macroexpand-1 will expand the macro call once and return it. A form is considered to be a macro call only if it is a cons whose car is a symbol for which a defmacro has been defined.

macroexpand is similar to macroexpand-1, but repeatedly expands form until it is no longer a macro call.

Macro: defmacro name lambda-list form …

When encountered by defmacro:eval, defmacro:macroexpand*, or defmacro:load defines a new macro which will henceforth be expanded when encountered by defmacro:eval, defmacro:macroexpand*, or defmacro:load.

3.1.1 Defmacroexpand

(require 'defmacroexpand)

Function: defmacro:expand* e

Returns the result of expanding all defmacros in scheme expression e.

3.2 R4RS Macros

(require 'macro) is the appropriate call if you want R4RS high-level macros but don't care about the low level implementation. If an SLIB R4RS macro implementation is already loaded it will be used. Otherwise, one of the R4RS macros implemetations is loaded.

The SLIB R4RS macro implementations support the following uniform interface:

Function: macro:expand sexpression

Takes an R4RS expression, macro-expands it, and returns the result of the macro expansion.

Function: macro:eval sexpression

Takes an R4RS expression, macro-expands it, evals the result of the macro expansion, and returns the result of the evaluation.

Procedure: macro:load filename

filename should be a string. If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially. These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

3.3 Macro by Example

(require 'macro-by-example)

A vanilla implementation of Macro by Example (Eugene Kohlbecker, R4RS) by Dorai Sitaram, (dorai @ cs.rice.edu) using defmacro.

• generating hygienic global define-syntax Macro-by-Example macros cheaply.
• can define macros which use ....
• needn't worry about a lexical variable in a macro definition clashing with a variable from the macro use context
• don't suffer the overhead of redefining the repl if defmacro natively supported (most implementations)

3.3.1 Caveat

These macros are not referentially transparent (see (r4rs)Macros section `Macros' in Revised(4) Scheme). Lexically scoped macros (i.e., let-syntax and letrec-syntax) are not supported. In any case, the problem of referential transparency gains poignancy only when let-syntax and letrec-syntax are used. So you will not be courting large-scale disaster unless you're using system-function names as local variables with unintuitive bindings that the macro can't use. However, if you must have the full r4rs macro functionality, look to the more featureful (but also more expensive) versions of syntax-rules available in slib Macros That Work, Syntactic Closures, and Syntax-Case Macros.

Macro: define-syntax keyword transformer-spec

The keyword is an identifier, and the transformer-spec should be an instance of syntax-rules.

The top-level syntactic environment is extended by binding the keyword to the specified transformer.

(define-syntax let* (syntax-rules () ((let* () body1 body2 ...) (let () body1 body2 ...)) ((let* ((name1 val1) (name2 val2) ...) body1 body2 ...) (let ((name1 val1)) (let* (( name2 val2) ...) body1 body2 ...)))))

Macro: syntax-rules literals syntax-rule …

literals is a list of identifiers, and each syntax-rule should be of the form

(pattern template)

where the pattern and template are as in the grammar above.

An instance of syntax-rules produces a new macro transformer by specifying a sequence of hygienic rewrite rules. A use of a macro whose keyword is associated with a transformer specified by syntax-rules is matched against the patterns contained in the syntax-rules, beginning with the leftmost syntax-rule. When a match is found, the macro use is trancribed hygienically according to the template.

Each pattern begins with the keyword for the macro. This keyword is not involved in the matching and is not considered a pattern variable or literal identifier.

3.4 Macros That Work

(require 'macros-that-work)

Macros That Work differs from the other R4RS macro implementations in that it does not expand derived expression types to primitive expression types.

Function: macro:expand expression

Function: macwork:expand expression

Takes an R4RS expression, macro-expands it, and returns the result of the macro expansion.

Function: macro:eval expression

Function: macwork:eval expression

macro:eval returns the value of expression in the current top level environment. expression can contain macro definitions. Side effects of expression will affect the top level environment.

Procedure: macro:load filename

Procedure: macwork:load filename

filename should be a string. If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially. These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

References:

The Revised^4 Report on the Algorithmic Language Scheme Clinger and Rees [editors]. To appear in LISP Pointers. Also available as a technical report from the University of Oregon, MIT AI Lab, and Cornell.

Macros That Work. Clinger and Rees. POPL '91.

The supported syntax differs from the R4RS in that vectors are allowed as patterns and as templates and are not allowed as pattern or template data.

transformer spec  →  (syntax-rules literals rules)

rules  →  ()
         |  (rule . rules)

rule  →  (pattern template)

pattern  →  pattern_var      ; a symbol not in literals
           |  symbol           ; a symbol in literals
           |  ()
           |  (pattern . pattern)
           |  (ellipsis_pattern)
           |  #(pattern*)                     ; extends R4RS
           |  #(pattern* ellipsis_pattern)    ; extends R4RS
           |  pattern_datum

template  →  pattern_var
            |  symbol
            |  ()
            |  (template2 . template2)
            |  #(template*)                   ; extends R4RS
            |  pattern_datum

template2  →  template
             |  ellipsis_template

pattern_datum  →  string                    ; no vector
                 |  character
                 |  boolean
                 |  number

ellipsis_pattern  → pattern ...

ellipsis_template  →  template ...

pattern_var  →  symbol   ; not in literals

literals  →  ()
            |  (symbol . literals)

3.4.1 Definitions

Scope of an ellipsis

Within a pattern or template, the scope of an ellipsis (...) is the pattern or template that appears to its left.

Rank of a pattern variable

The rank of a pattern variable is the number of ellipses within whose scope it appears in the pattern.

Rank of a subtemplate

The rank of a subtemplate is the number of ellipses within whose scope it appears in the template.

Template rank of an occurrence of a pattern variable

The template rank of an occurrence of a pattern variable within a template is the rank of that occurrence, viewed as a subtemplate.

Variables bound by a pattern

The variables bound by a pattern are the pattern variables that appear within it.

Referenced variables of a subtemplate

The referenced variables of a subtemplate are the pattern variables that appear within it.

Variables opened by an ellipsis template

The variables opened by an ellipsis template are the referenced pattern variables whose rank is greater than the rank of the ellipsis template.

3.4.2 Restrictions

No pattern variable appears more than once within a pattern.

For every occurrence of a pattern variable within a template, the template rank of the occurrence must be greater than or equal to the pattern variable's rank.

Every ellipsis template must open at least one variable.

For every ellipsis template, the variables opened by an ellipsis template must all be bound to sequences of the same length.

The compiled form of a rule is

rule  →  (pattern template inserted)

pattern  →  pattern_var
           |  symbol
           |  ()
           |  (pattern . pattern)
           |  ellipsis_pattern
           |  #(pattern)
           |  pattern_datum

template  →  pattern_var
            |  symbol
            |  ()
            |  (template2 . template2)
            |  #(pattern)
            |  pattern_datum

template2  →  template
             |  ellipsis_template

pattern_datum  →  string
                 |  character
                 |  boolean
                 |  number

pattern_var  →  #(V symbol rank)

ellipsis_pattern  →  #(E pattern pattern_vars)

ellipsis_template  →  #(E template pattern_vars)

inserted  →  ()
            |  (symbol . inserted)

pattern_vars  →  ()
                |  (pattern_var . pattern_vars)

rank  →  exact non-negative integer

where V and E are unforgeable values.

The pattern variables associated with an ellipsis pattern are the variables bound by the pattern, and the pattern variables associated with an ellipsis template are the variables opened by the ellipsis template.

If the template contains a big chunk that contains no pattern variables or inserted identifiers, then the big chunk will be copied unnecessarily. That shouldn't matter very often.

3.5 Syntactic Closures

(require 'syntactic-closures)

Function: macro:expand expression

Function: synclo:expand expression

Returns scheme code with the macros and derived expression types of expression expanded to primitive expression types.

Function: macro:eval expression

Function: synclo:eval expression

macro:eval returns the value of expression in the current top level environment. expression can contain macro definitions. Side effects of expression will affect the top level environment.

Procedure: macro:load filename

Procedure: synclo:load filename

filename should be a string. If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially. These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

3.5.1 Syntactic Closure Macro Facility

A Syntactic Closures Macro Facility

by Chris Hanson

9 November 1991

This document describes syntactic closures, a low-level macro facility for the Scheme programming language. The facility is an alternative to the low-level macro facility described in the Revised^4 Report on Scheme. This document is an addendum to that report.

The syntactic closures facility extends the BNF rule for transformer spec to allow a new keyword that introduces a low-level macro transformer:

transformer spec := (transformer expression)

Additionally, the following procedures are added:

make-syntactic-closure
capture-syntactic-environment
identifier?
identifier=?

The description of the facility is divided into three parts. The first part defines basic terminology. The second part describes how macro transformers are defined. The third part describes the use of identifiers, which extend the syntactic closure mechanism to be compatible with syntax-rules.

3.5.1.1 Terminology

This section defines the concepts and data types used by the syntactic closures facility.

• Forms are the syntactic entities out of which programs are recursively constructed. A form is any expression, any definition, any syntactic keyword, or any syntactic closure. The variable name that appears in a set! special form is also a form. Examples of forms:

  17 #t car (+ x 4) (lambda (x) x) (define pi 3.14159) if define

• An alias is an alternate name for a given symbol. It can appear anywhere in a form that the symbol could be used, and when quoted it is replaced by the symbol; however, it does not satisfy the predicate symbol?. Macro transformers rarely distinguish symbols from aliases, referring to both as identifiers.
• A syntactic environment maps identifiers to their meanings. More precisely, it determines whether an identifier is a syntactic keyword or a variable. If it is a keyword, the meaning is an interpretation for the form in which that keyword appears. If it is a variable, the meaning identifies which binding of that variable is referenced. In short, syntactic environments contain all of the contextual information necessary for interpreting the meaning of a particular form.
• A syntactic closure consists of a form, a syntactic environment, and a list of identifiers. All identifiers in the form take their meaning from the syntactic environment, except those in the given list. The identifiers in the list are to have their meanings determined later. A syntactic closure may be used in any context in which its form could have been used. Since a syntactic closure is also a form, it may not be used in contexts where a form would be illegal. For example, a form may not appear as a clause in the cond special form. A syntactic closure appearing in a quoted structure is replaced by its form.

3.5.1.2 Transformer Definition

This section describes the transformer special form and the procedures make-syntactic-closure and capture-syntactic-environment.

Syntax: transformer expression

Syntax: It is an error if this syntax occurs except as a transformer spec.

Semantics: The expression is evaluated in the standard transformer environment to yield a macro transformer as described below. This macro transformer is bound to a macro keyword by the special form in which the transformer expression appears (for example, let-syntax).

A macro transformer is a procedure that takes two arguments, a form and a syntactic environment, and returns a new form. The first argument, the input form, is the form in which the macro keyword occurred. The second argument, the usage environment, is the syntactic environment in which the input form occurred. The result of the transformer, the output form, is automatically closed in the transformer environment, which is the syntactic environment in which the transformer expression occurred.

For example, here is a definition of a push macro using syntax-rules:

(define-syntax push (syntax-rules () ((push item list) (set! list (cons item list)))))

Here is an equivalent definition using transformer:

(define-syntax push (transformer (lambda (exp env) (let ((item (make-syntactic-closure env '() (cadr exp))) (list (make-syntactic-closure env '() (caddr exp)))) `(set! ,list (cons ,item ,list))))))

In this example, the identifiers set! and cons are closed in the transformer environment, and thus will not be affected by the meanings of those identifiers in the usage environment env.

Some macros may be non-hygienic by design. For example, the following defines a loop macro that implicitly binds exit to an escape procedure. The binding of exit is intended to capture free references to exit in the body of the loop, so exit must be left free when the body is closed:

(define-syntax loop (transformer (lambda (exp env) (let ((body (cdr exp))) `(call-with-current-continuation (lambda (exit) (let f () ,@(map (lambda (exp) (make-syntactic-closure env '(exit) exp)) body) (f))))))))

To assign meanings to the identifiers in a form, use make-syntactic-closure to close the form in a syntactic environment.

Function: make-syntactic-closure environment free-names form

environment must be a syntactic environment, free-names must be a list of identifiers, and form must be a form. make-syntactic-closure constructs and returns a syntactic closure of form in environment, which can be used anywhere that form could have been used. All the identifiers used in form, except those explicitly excepted by free-names, obtain their meanings from environment.

Here is an example where free-names is something other than the empty list. It is instructive to compare the use of free-names in this example with its use in the loop example above: the examples are similar except for the source of the identifier being left free.

(define-syntax let1 (transformer (lambda (exp env) (let ((id (cadr exp)) (init (caddr exp)) (exp (cadddr exp))) `((lambda (,id) ,(make-syntactic-closure env (list id) exp)) ,(make-syntactic-closure env '() init))))))

let1 is a simplified version of let that only binds a single identifier, and whose body consists of a single expression. When the body expression is syntactically closed in its original syntactic environment, the identifier that is to be bound by let1 must be left free, so that it can be properly captured by the lambda in the output form.

To obtain a syntactic environment other than the usage environment, use capture-syntactic-environment.

Function: capture-syntactic-environment procedure

capture-syntactic-environment returns a form that will, when transformed, call procedure on the current syntactic environment. procedure should compute and return a new form to be transformed, in that same syntactic environment, in place of the form.

An example will make this clear. Suppose we wanted to define a simple loop-until keyword equivalent to

(define-syntax loop-until (syntax-rules () ((loop-until id init test return step) (letrec ((loop (lambda (id) (if test return (loop step))))) (loop init)))))

The following attempt at defining loop-until has a subtle bug:

(define-syntax loop-until (transformer (lambda (exp env) (let ((id (cadr exp)) (init (caddr exp)) (test (cadddr exp)) (return (cadddr (cdr exp))) (step (cadddr (cddr exp))) (close (lambda (exp free) (make-syntactic-closure env free exp)))) `(letrec ((loop (lambda (,id) (if ,(close test (list id)) ,(close return (list id)) (loop ,(close step (list id))))))) (loop ,(close init '())))))))

This definition appears to take all of the proper precautions to prevent unintended captures. It carefully closes the subexpressions in their original syntactic environment and it leaves the id identifier free in the test, return, and step expressions, so that it will be captured by the binding introduced by the lambda expression. Unfortunately it uses the identifiers if and loop within that lambda expression, so if the user of loop-until just happens to use, say, if for the identifier, it will be inadvertently captured.

The syntactic environment that if and loop want to be exposed to is the one just outside the lambda expression: before the user's identifier is added to the syntactic environment, but after the identifier loop has been added. capture-syntactic-environment captures exactly that environment as follows:

(define-syntax loop-until (transformer (lambda (exp env) (let ((id (cadr exp)) (init (caddr exp)) (test (cadddr exp)) (return (cadddr (cdr exp))) (step (cadddr (cddr exp))) (close (lambda (exp free) (make-syntactic-closure env free exp)))) `(letrec ((loop ,(capture-syntactic-environment (lambda (env) `(lambda (,id) (,(make-syntactic-closure env '() `if) ,(close test (list id)) ,(close return (list id)) (,(make-syntactic-closure env '() `loop) ,(close step (list id))))))))) (loop ,(close init '())))))))

In this case, having captured the desired syntactic environment, it is convenient to construct syntactic closures of the identifiers if and the loop and use them in the body of the lambda.

A common use of capture-syntactic-environment is to get the transformer environment of a macro transformer:

(transformer (lambda (exp env) (capture-syntactic-environment (lambda (transformer-env) ...))))

3.5.1.3 Identifiers

This section describes the procedures that create and manipulate identifiers. Previous syntactic closure proposals did not have an identifier data type - they just used symbols. The identifier data type extends the syntactic closures facility to be compatible with the high-level syntax-rules facility.

As discussed earlier, an identifier is either a symbol or an alias. An alias is implemented as a syntactic closure whose form is an identifier:

(make-syntactic-closure env '() 'a)
   ⇒ an alias

Aliases are implemented as syntactic closures because they behave just like syntactic closures most of the time. The difference is that an alias may be bound to a new value (for example by lambda or let-syntax); other syntactic closures may not be used this way. If an alias is bound, then within the scope of that binding it is looked up in the syntactic environment just like any other identifier.

Aliases are used in the implementation of the high-level facility syntax-rules. A macro transformer created by syntax-rules uses a template to generate its output form, substituting subforms of the input form into the template. In a syntactic closures implementation, all of the symbols in the template are replaced by aliases closed in the transformer environment, while the output form itself is closed in the usage environment. This guarantees that the macro transformation is hygienic, without requiring the transformer to know the syntactic roles of the substituted input subforms.

Function: identifier? object

Returns #t if object is an identifier, otherwise returns #f. Examples:

(identifier? 'a) ⇒ #t (identifier? (make-syntactic-closure env '() 'a)) ⇒ #t (identifier? "a") ⇒ #f (identifier? #\a) ⇒ #f (identifier? 97) ⇒ #f (identifier? #f) ⇒ #f (identifier? '(a)) ⇒ #f (identifier? '#(a)) ⇒ #f

The predicate eq? is used to determine if two identifers are "the same". Thus eq? can be used to compare identifiers exactly as it would be used to compare symbols. Often, though, it is useful to know whether two identifiers "mean the same thing". For example, the cond macro uses the symbol else to identify the final clause in the conditional. A macro transformer for cond cannot just look for the symbol else, because the cond form might be the output of another macro transformer that replaced the symbol else with an alias. Instead the transformer must look for an identifier that "means the same thing" in the usage environment as the symbol else means in the transformer environment.

Function: identifier=? environment1 identifier1 environment2 identifier2

environment1 and environment2 must be syntactic environments, and identifier1 and identifier2 must be identifiers. identifier=? returns #t if the meaning of identifier1 in environment1 is the same as that of identifier2 in environment2, otherwise it returns #f. Examples:

(let-syntax ((foo (transformer (lambda (form env) (capture-syntactic-environment (lambda (transformer-env) (identifier=? transformer-env 'x env 'x))))))) (list (foo) (let ((x 3)) (foo)))) ⇒ (#t #f)

(let-syntax ((bar foo)) (let-syntax ((foo (transformer (lambda (form env) (capture-syntactic-environment (lambda (transformer-env) (identifier=? transformer-env 'foo env (cadr form)))))))) (list (foo foo) (foobar)))) ⇒ (#f #t)

3.5.1.4 Acknowledgements

The syntactic closures facility was invented by Alan Bawden and Jonathan Rees. The use of aliases to implement syntax-rules was invented by Alan Bawden (who prefers to call them synthetic names). Much of this proposal is derived from an earlier proposal by Alan Bawden.

3.6 Syntax-Case Macros

(require 'syntax-case)

Function: macro:expand expression

Function: syncase:expand expression

Returns scheme code with the macros and derived expression types of expression expanded to primitive expression types.

Function: macro:eval expression

Function: syncase:eval expression

macro:eval returns the value of expression in the current top level environment. expression can contain macro definitions. Side effects of expression will affect the top level environment.

Procedure: macro:load filename

Procedure: syncase:load filename

filename should be a string. If filename names an existing file, the macro:load procedure reads Scheme source code expressions and definitions from the file and evaluates them sequentially. These source code expressions and definitions may contain macro definitions. The macro:load procedure does not affect the values returned by current-input-port and current-output-port.

This is version 2.1 of syntax-case, the low-level macro facility proposed and implemented by Robert Hieb and R. Kent Dybvig.

This version is further adapted by Harald Hanche-Olsen <hanche @ imf.unit.no> to make it compatible with, and easily usable with, SLIB. Mainly, these adaptations consisted of:

• Removing white space from `expand.pp' to save space in the distribution. This file is not meant for human readers anyway…
• Removed a couple of Chez scheme dependencies.
• Renamed global variables used to minimize the possibility of name conflicts.
• Adding an SLIB-specific initialization file.
• Removing a couple extra files, most notably the documentation (but see below).

If you wish, you can see exactly what changes were done by reading the shell script in the file `syncase.sh'.

The two PostScript files were omitted in order to not burden the SLIB distribution with them. If you do intend to use syntax-case, however, you should get these files and print them out on a PostScript printer. They are available with the original syntax-case distribution by anonymous FTP in `cs.indiana.edu:/pub/scheme/syntax-case'.

In order to use syntax-case from an interactive top level, execute:

(require 'syntax-case)
(require 'repl)
(repl:top-level macro:eval)

See the section Repl (see section Repl) for more information.

To check operation of syntax-case get `cs.indiana.edu:/pub/scheme/syntax-case', and type

(require 'syntax-case)
(syncase:sanity-check)

Beware that syntax-case takes a long time to load - about 20s on a SPARCstation SLC (with SCM) and about 90s on a Macintosh SE/30 (with Gambit).

3.6.1 Notes

All R4RS syntactic forms are defined, including delay. Along with delay are simple definitions for make-promise (into which delay expressions expand) and force.

syntax-rules and with-syntax (described in TR356) are defined.

syntax-case is actually defined as a macro that expands into calls to the procedure syntax-dispatch and the core form syntax-lambda; do not redefine these names.

Several other top-level bindings not documented in TR356 are created:

• the "hooks" in `hooks.ss'
• the build- procedures in `output.ss'
• expand-syntax (the expander)

The syntax of define has been extended to allow (define id), which assigns id to some unspecified value.

We have attempted to maintain R4RS compatibility where possible. The incompatibilities should be confined to `hooks.ss'. Please let us know if there is some incompatibility that is not flagged as such.

Send bug reports, comments, suggestions, and questions to Kent Dybvig (dyb @ iuvax.cs.indiana.edu).

3.6.2 Note from SLIB maintainer

(require 'structure)

Included with the syntax-case files was `structure.scm' which defines a macro define-structure. I have no documentation for this macro; it is not used by any other code in SLIB.

3.7 Fluid-Let

(require 'fluid-let)

Syntax: fluid-let (bindings …) forms…

(fluid-let ((variable init) …)
   expression expression …)

The inits are evaluated in the current environment (in some unspecified order), the current values of the variables are saved, the results are assigned to the variables, the expressions are evaluated sequentially in the current environment, the variables are restored to their original values, and the value of the last expression is returned.

The syntax of this special form is similar to that of let, but fluid-let temporarily rebinds existing variables. Unlike let, fluid-let creates no new bindings; instead it assigns the values of each init to the binding (determined by the rules of lexical scoping) of its corresponding variable.

3.8 Yasos

(require 'oop) or (require 'yasos)

`Yet Another Scheme Object System' is a simple object system for Scheme based on the paper by Norman Adams and Jonathan Rees: Object Oriented Programming in Scheme, Proceedings of the 1988 ACM Conference on LISP and Functional Programming, July 1988 [ACM #552880].

Another reference is:

Ken Dickey. <A HREF="ftp://ftp.cs.indiana.edu/pub/scheme-repository/doc/pubs/swob.txt"> Scheming with Objects </A> AI Expert Volume 7, Number 10 (October 1992), pp. 24-33.

3.8.1 Terms

Object

Any Scheme data object.

Instance

An instance of the OO system; an object.

Operation

A method.

Notes:

The object system supports multiple inheritance. An instance can inherit from 0 or more ancestors. In the case of multiple inherited operations with the same identity, the operation used is that from the first ancestor which contains it (in the ancestor let). An operation may be applied to any Scheme data object--not just instances. As code which creates instances is just code, there are no classes and no meta-anything. Method dispatch is by a procedure call a la CLOS rather than by send syntax a la Smalltalk.

Disclaimer:

There are a number of optimizations which can be made. This implementation is expository (although performance should be quite reasonable). See the L&FP paper for some suggestions.

3.8.2 Interface

Syntax: define-operation (opname self arg …) default-body

Defines a default behavior for data objects which don't handle the operation opname. The default behavior (for an empty default-body) is to generate an error.

Syntax: define-predicate opname?

Defines a predicate opname?, usually used for determining the type of an object, such that (opname? object) returns #t if object has an operation opname? and #f otherwise.

Syntax: object ((name self arg …) body) …

Returns an object (an instance of the object system) with operations. Invoking (name object arg … executes the body of the object with self bound to object and with argument(s) arg….

Syntax: object-with-ancestors ((ancestor1 init1) …) operation …

A let-like form of object for multiple inheritance. It returns an object inheriting the behaviour of ancestor1 etc. An operation will be invoked in an ancestor if the object itself does not provide such a method. In the case of multiple inherited operations with the same identity, the operation used is the one found in the first ancestor in the ancestor list.

Syntax: operate-as component operation self arg …

Used in an operation definition (of self) to invoke the operation in an ancestor component but maintain the object's identity. Also known as "send-to-super".

Procedure: print obj port

A default print operation is provided which is just (format port obj) (see section Format (version 3.0)) for non-instances and prints obj preceded by `#<INSTANCE>' for instances.

Function: size obj

The default method returns the number of elements in obj if it is a vector, string or list, 2 for a pair, 1 for a character and by default id an error otherwise. Objects such as collections (see section Collections) may override the default in an obvious way.

3.8.3 Setters

Setters implement generalized locations for objects associated with some sort of mutable state. A getter operation retrieves a value from a generalized location and the corresponding setter operation stores a value into the location. Only the getter is named - the setter is specified by a procedure call as below. (Dylan uses special syntax.) Typically, but not necessarily, getters are access operations to extract values from Yasos objects (see section Yasos). Several setters are predefined, corresponding to getters car, cdr, string-ref and vector-ref e.g., (setter car) is equivalent to set-car!.

This implementation of setters is similar to that in Dylan(TM) (Dylan: An object-oriented dynamic language, Apple Computer Eastern Research and Technology). Common LISP provides similar facilities through setf.

Function: setter getter

Returns the setter for the procedure getter. E.g., since string-ref is the getter corresponding to a setter which is actually string-set!:

(define foo "foo") ((setter string-ref) foo 0 #\F) ; set element 0 of foo foo ⇒ "Foo"

Syntax: set place new-value

If place is a variable name, set is equivalent to set!. Otherwise, place must have the form of a procedure call, where the procedure name refers to a getter and the call indicates an accessible generalized location, i.e., the call would return a value. The return value of set is usually unspecified unless used with a setter whose definition guarantees to return a useful value.

(set (string-ref foo 2) #\O) ; generalized location with getter foo ⇒ "FoO" (set foo "foo") ; like set! foo ⇒ "foo"

Procedure: add-setter getter setter

Add procedures getter and setter to the (inaccessible) list of valid setter/getter pairs. setter implements the store operation corresponding to the getter access operation for the relevant state. The return value is unspecified.

Procedure: remove-setter-for getter

Removes the setter corresponding to the specified getter from the list of valid setters. The return value is unspecified.

Syntax: define-access-operation getter-name

Shorthand for a Yasos define-operation defining an operation getter-name that objects may support to return the value of some mutable state. The default operation is to signal an error. The return value is unspecified.

3.8.4 Examples

;;; These definitions for PRINT and SIZE are
;;; already supplied by
(require 'yasos)

(define-operation (print obj port)
  (format port
          (if (instance? obj) "#<instance>" "~s")
          obj))

(define-operation (size obj)
  (cond
   ((vector? obj) (vector-length obj))
   ((list?   obj) (length obj))
   ((pair?   obj) 2)
   ((string? obj) (string-length obj))
   ((char?   obj) 1)
   (else
    (slib:error "Operation not supported: size" obj))))

(define-predicate cell?)
(define-operation (fetch obj))
(define-operation (store! obj newValue))

(define (make-cell value)
  (object
   ((cell? self) #t)
   ((fetch self) value)
   ((store! self newValue)
    (set! value newValue)
    newValue)
   ((size self) 1)
   ((print self port)
    (format port "#<Cell: ~s>" (fetch self)))))

(define-operation (discard obj value)
  (format #t "Discarding ~s~%" value))

(define (make-filtered-cell value filter)
  (object-with-ancestors
   ((cell (make-cell value)))
   ((store! self newValue)
   (if (filter newValue)
       (store! cell newValue)
       (discard self newValue)))))

(define-predicate array?)
(define-operation (array-ref array index))
(define-operation (array-set! array index value))

(define (make-array num-slots)
  (let ((anArray (make-vector num-slots)))
    (object
     ((array? self) #t)
     ((size self) num-slots)
     ((array-ref self index)
      (vector-ref  anArray index))
     ((array-set! self index newValue)
      (vector-set! anArray index newValue))
     ((print self port)
      (format port "#<Array ~s>" (size self))))))

(define-operation (position obj))
(define-operation (discarded-value obj))

(define (make-cell-with-history value filter size)
  (let ((pos 0) (most-recent-discard #f))
    (object-with-ancestors
     ((cell (make-filtered-call value filter))
      (sequence (make-array size)))
     ((array? self) #f)
     ((position self) pos)
     ((store! self newValue)
      (operate-as cell store! self newValue)
      (array-set! self pos newValue)
      (set! pos (+ pos 1)))
     ((discard self value)
      (set! most-recent-discard value))
     ((discarded-value self) most-recent-discard)
     ((print self port)
      (format port "#<Cell-with-history ~s>"
              (fetch self))))))

(define-access-operation fetch)
(add-setter fetch store!)
(define foo (make-cell 1))
(print foo #f)
⇒ "#<Cell: 1>"
(set (fetch foo) 2)
⇒
(print foo #f)
⇒ "#<Cell: 2>"
(fetch foo)
⇒ 2

4. Textual Conversion Packages

4.1 Precedence Parsing

(require 'precedence-parse) or (require 'parse)

This package implements:

• a Pratt style precedence parser;
• a tokenizer which congeals tokens according to assigned classes of constituent characters;
• procedures giving direct control of parser rulesets;
• procedures for higher level specification of rulesets.

4.1.1 Precedence Parsing Overview

This package offers improvements over previous parsers.

• Common computer language constructs are concisely specified.
• Grammars can be changed dynamically. Operators can be assigned different meanings within a lexical context.
• Rulesets don't need compilation. Grammars can be changed incrementally.
• Operator precedence is specified by integers.
• All possibilities of bad input are handled (3) and return as much structure as was parsed when the error occured; The symbol ? is substituted for missing input.

The notion of binding power may be unfamiliar to those accustomed to BNF grammars.

When two consecutive objects are parsed, the first might be the prefix to the second, or the second might be a suffix of the first. Comparing the left and right binding powers of the two objects decides which way to interpret them.

Objects at each level of syntactic grouping have binding powers.

A syntax tree is not built unless the rules explicitly do so. The call graph of grammar rules effectively instantiate the sytnax tree.

The JACAL symbolic math system (http://swissnet.ai.mit.edu/~jaffer/JACAL.html) uses precedence-parse. Its grammar definitions in the file `jacal/English.scm' can serve as examples of use.

4.1.2 Rule Types

Here are the higher-level syntax types and an example of each. Precedence considerations are omitted for clarity. See Grammar Rule Definition for full details.

Grammar: nofix bye exit

bye

calls the function exit with no arguments.

Grammar: prefix - negate

- 42

Calls the function negate with the argument 42.

Grammar: infix - difference

x - y

Calls the function difference with arguments x and y.

Grammar: nary + sum

x + y + z

Calls the function sum with arguments x, y, and y.

Grammar: postfix ! factorial

5 !

Calls the function factorial with the argument 5.

Grammar: prestfix set set!

set foo bar

Calls the function set! with the arguments foo and bar.

Grammar: commentfix /* */

/* almost any text here */

Ignores the comment delimited by /* and */.

Grammar: matchfix { list }

{0, 1, 2}

Calls the function list with the arguments 0, 1, and 2.

Grammar: inmatchfix ( funcall )

f(x, y)

Calls the function funcall with the arguments f, x, and y.

Grammar: delim ;

set foo bar;

delimits the extent of the restfix operator set.

4.1.3 Ruleset Definition and Use

Variable: *syn-defs*

A grammar is built by one or more calls to prec:define-grammar. The rules are appended to *syn-defs*. The value of *syn-defs* is the grammar suitable for passing as an argument to prec:parse.

Constant: *syn-ignore-whitespace*

Is a nearly empty grammar with whitespace characters set to group 0, which means they will not be made into tokens. Most rulesets will want to start with *syn-ignore-whitespace*

In order to start defining a grammar, either

(set! *syn-defs* '())

or

(set! *syn-defs* *syn-ignore-whitespace*)

Function: prec:define-grammar rule1 …

Appends rule1 … to *syn-defs*. prec:define-grammar is used to define both the character classes and rules for tokens.

Once your grammar is defined, save the value of *syn-defs* in a variable (for use when calling prec:parse).

(define my-ruleset *syn-defs*)

Function: prec:parse ruleset delim

Function: prec:parse ruleset delim port

The ruleset argument must be a list of rules as constructed by prec:define-grammar and extracted from *syn-defs*.

The token delim may be a character, symbol, or string. A character delim argument will match only a character token; i.e. a character for which no token-group is assigned. A symbols or string will match only a token string; i.e. a token resulting from a token group.

prec:parse reads a ruleset grammar expression delimited by delim from the given input port. prec:parse returns the next object parsable from the given input port, updating port to point to the first character past the end of the external representation of the object.

If an end of file is encountered in the input before any characters are found that can begin an object, then an end of file object is returned. If a delimiter (such as delim) is found before any characters are found that can begin an object, then #f is returned.

The port argument may be omitted, in which case it defaults to the value returned by current-input-port. It is an error to parse from a closed port.

4.1.4 Token definition

Function: tok:char-group group chars chars-proc

The argument chars may be a single character, a list of characters, or a string. Each character in chars is treated as though tok:char-group was called with that character alone.

The argument chars-proc must be a procedure of one argument, a list of characters. After tokenize has finished accumulating the characters for a token, it calls chars-proc with the list of characters. The value returned is the token which tokenize returns.

The argument group may be an exact integer or a procedure of one character argument. The following discussion concerns the treatment which the tokenizing routine, tokenize, will accord to characters on the basis of their groups.

When group is a non-zero integer, characters whose group number is equal to or exactly one less than group will continue to accumulate. Any other character causes the accumulation to stop (until a new token is to be read).

The group of zero is special. These characters are ignored when parsed pending a token, and stop the accumulation of token characters when the accumulation has already begun. Whitespace characters are usually put in group 0.

If group is a procedure, then, when triggerd by the occurence of an initial (no accumulation) chars character, this procedure will be repeatedly called with each successive character from the input stream until the group procedure returns a non-false value.

The following convenient constants are provided for use with tok:char-group.

Constant: tok:decimal-digits

Is the string "0123456789".

Constant: tok:upper-case

Is the string consisting of all upper-case letters ("ABCDEFGHIJKLMNOPQRSTUVWXYZ").

Constant: tok:lower-case

Is the string consisting of all lower-case letters ("abcdefghijklmnopqrstuvwxyz").

Constant: tok:whitespaces

Is the string consisting of all characters between 0 and 255 for which char-whitespace? returns true.

For the purpose of reporting problems in error messages, this package keeps track of the current column. When the column does not simply track input characters, tok:bump-column can be used to adjust the current-column.

Function: tok:bump-column pos port

Adds pos to the current-column for input-port port.

4.1.5 Nud and Led Definition

This section describes advanced features. You can skip this section on first reading.

The Null Denotation (or nud) of a token is the procedure and arguments applying for that token when Left, an unclaimed parsed expression is not extant.

The Left Denotation (or led) of a token is the procedure, arguments, and lbp applying for that token when there is a Left, an unclaimed parsed expression.

In his paper,

Pratt, V. R. Top Down Operator Precendence. SIGACT/SIGPLAN Symposium on Principles of Programming Languages, Boston, 1973, pages 41-51

the left binding power (or lbp) was an independent property of tokens. I think this was done in order to allow tokens with NUDs but not LEDs to also be used as delimiters, which was a problem for statically defined syntaxes. It turns out that dynamically binding NUDs and LEDs allows them independence.

For the rule-defining procedures that follow, the variable tk may be a character, string, or symbol, or a list composed of characters, strings, and symbols. Each element of tk is treated as though the procedure were called for each element.

Character tk arguments will match only character tokens; i.e. characters for which no token-group is assigned. Symbols and strings will both match token strings; i.e. tokens resulting from token groups.

Function: prec:make-nud tk sop arg1 …

Returns a rule specifying that sop be called when tk is parsed. If sop is a procedure, it is called with tk and arg1 … as its arguments; the resulting value is incorporated into the expression being built. Otherwise, (list sop arg1 …) is incorporated.

If no NUD has been defined for a token; then if that token is a string, it is converted to a symbol and returned; if not a string, the token is returned.

Function: prec:make-led tk sop arg1 …

Returns a rule specifying that sop be called when tk is parsed and left has an unclaimed parsed expression. If sop is a procedure, it is called with left, tk, and arg1 … as its arguments; the resulting value is incorporated into the expression being built. Otherwise, left is incorporated.

If no LED has been defined for a token, and left is set, the parser issues a warning.

4.1.6 Grammar Rule Definition

Here are procedures for defining rules for the syntax types introduced in Precedence Parsing Overview.

For the rule-defining procedures that follow, the variable tk may be a character, string, or symbol, or a list composed of characters, strings, and symbols. Each element of tk is treated as though the procedure were called for each element.

For procedures prec:delim, …, prec:prestfix, if the sop argument is #f, then the token which triggered this rule is converted to a symbol and returned. A false sop argument to the procedures prec:commentfix, prec:matchfix, or prec:inmatchfix has a different meaning.

Character tk arguments will match only character tokens; i.e. characters for which no token-group is assigned. Symbols and strings will both match token strings; i.e. tokens resulting from token groups.

Function: prec:delim tk

Returns a rule specifying that tk should not be returned from parsing; i.e. tk's function is purely syntactic. The end-of-file is always treated as a delimiter.

Function: prec:nofix tk sop

Returns a rule specifying the following actions take place when tk is parsed:

• If sop is a procedure, it is called with no arguments; the resulting value is incorporated into the expression being built. Otherwise, the list of sop is incorporated.

Function: prec:prefix tk sop bp rule1 …

Returns a rule specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• prec:parse1 is called with binding-power bp.
• If sop is a procedure, it is called with the expression returned from prec:parse1; the resulting value is incorporated into the expression being built. Otherwise, the list of sop and the expression returned from prec:parse1 is incorporated.
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

Function: prec:infix tk sop lbp bp rule1 …

Returns a rule declaring the left-binding-precedence of the token tk is lbp and specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• One expression is parsed with binding-power lbp. If instead a delimiter is encountered, a warning is issued.
• If sop is a procedure, it is applied to the list of left and the parsed expression; the resulting value is incorporated into the expression being built. Otherwise, the list of sop, the left expression, and the parsed expression is incorporated.
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

Function: prec:nary tk sop bp

Returns a rule declaring the left-binding-precedence of the token tk is bp and specifying the following actions take place when tk is parsed:

• Expressions are parsed with binding-power bp as far as they are interleaved with the token tk.
• If sop is a procedure, it is applied to the list of left and the parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of sop, the left expression, and the parsed expressions is incorporated.

Function: prec:postfix tk sop lbp

Returns a rule declaring the left-binding-precedence of the token tk is lbp and specifying the following actions take place when tk is parsed:

• If sop is a procedure, it is called with the left expression; the resulting value is incorporated into the expression being built. Otherwise, the list of sop and the left expression is incorporated.

Function: prec:prestfix tk sop bp rule1 …

Returns a rule specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• Expressions are parsed with binding-power bp until a delimiter is reached.
• If sop is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of sop and the parsed expressions is incorporated.
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

Function: prec:commentfix tk stp match rule1 …

Returns rules specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• Characters are read until and end-of-file or a sequence of characters is read which matches the string match.
• If stp is a procedure, it is called with the string of all that was read between the tk and match (exclusive).
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

Parsing of commentfix syntax differs from the others in several ways. It reads directly from input without tokenizing; It calls stp but does not return its value; nay any value. I added the stp argument so that comment text could be echoed.

Function: prec:matchfix tk sop sep match rule1 …

Returns a rule specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• A rule declaring the token match a delimiter takes effect.
• Expressions are parsed with binding-power 0 until the token match is reached. If the token sep does not appear between each pair of expressions parsed, a warning is issued.
• If sop is a procedure, it is applied to the list of parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of sop and the parsed expressions is incorporated.
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

Function: prec:inmatchfix tk sop sep match lbp rule1 …

Returns a rule declaring the left-binding-precedence of the token tk is lbp and specifying the following actions take place when tk is parsed:

• The rules rule1 … augment and, in case of conflict, override rules currently in effect.
• A rule declaring the token match a delimiter takes effect.
• Expressions are parsed with binding-power 0 until the token match is reached. If the token sep does not appear between each pair of expressions parsed, a warning is issued.
• If sop is a procedure, it is applied to the list of left and the parsed expressions; the resulting value is incorporated into the expression being built. Otherwise, the list of sop, the left expression, and the parsed expressions is incorporated.
• The ruleset in effect before tk was parsed is restored; rule1 … are forgotten.

4.2 Format (version 3.0)

<A NAME="format"></A>

The `format.scm' package was removed because it was not reentrant. http://swissnet.ai.mit.edu/~jaffer/SLIB.FAQ explains more about FORMAT's woes.

4.3 Standard Formatted I/O

4.3.1 stdio

(require 'stdio)

requires printf and scanf and additionally defines the symbols:

Variable: stdin

Defined to be (current-input-port).

Variable: stdout

Defined to be (current-output-port).

Variable: stderr

Defined to be (current-error-port).

4.3.2 Standard Formatted Output

<A NAME="printf"></A> (require 'printf)

Procedure: printf format arg1 …

Procedure: fprintf port format arg1 …

Procedure: sprintf str format arg1 …

Procedure: sprintf #f format arg1 …

Procedure: sprintf k format arg1 …

Each function converts, formats, and outputs its arg1 … arguments according to the control string format argument and returns the number of characters output.

printf sends its output to the port (current-output-port). fprintf sends its output to the port port. sprintf string-set!s locations of the non-constant string argument str to the output characters.

Two extensions of sprintf return new strings. If the first argument is #f, then the returned string's length is as many characters as specified by the format and data; if the first argument is a non-negative integer k, then the length of the returned string is also bounded by k.

The string format contains plain characters which are copied to the output stream, and conversion specifications, each of which results in fetching zero or more of the arguments arg1 …. The results are undefined if there are an insufficient number of arguments for the format. If format is exhausted while some of the arg1 … arguments remain unused, the excess arg1 … arguments are ignored.

The conversion specifications in a format string have the form:

% [ flags ] [ width ] [ . precision ] [ type ] conversion

An output conversion specifications consist of an initial `%' character followed in sequence by:

• Zero or more flag characters that modify the normal behavior of the conversion specification.

  `-'

  Left-justify the result in the field. Normally the result is right-justified.

  `+'

  For the signed `%d' and `%i' conversions and all inexact conversions, prefix a plus sign if the value is positive.

  ` '

  For the signed `%d' and `%i' conversions, if the result doesn't start with a plus or minus sign, prefix it with a space character instead. Since the `+' flag ensures that the result includes a sign, this flag is ignored if both are specified.

  `#'

  For inexact conversions, `#' specifies that the result should always include a decimal point, even if no digits follow it. For the `%g' and `%G' conversions, this also forces trailing zeros after the decimal point to be printed where they would otherwise be elided.

  For the `%o' conversion, force the leading digit to be `0', as if by increasing the precision. For `%x' or `%X', prefix a leading `0x' or `0X' (respectively) to the result. This doesn't do anything useful for the `%d', `%i', or `%u' conversions. Using this flag produces output which can be parsed by the scanf functions with the `%i' conversion (see section Standard Formatted Input).

  `0'

  Pad the field with zeros instead of spaces. The zeros are placed after any indication of sign or base. This flag is ignored if the `-' flag is also specified, or if a precision is specified for an exact converson.

• An optional decimal integer specifying the minimum field width. If the normal conversion produces fewer characters than this, the field is padded (with spaces or zeros per the `0' flag) to the specified width. This is a minimum width; if the normal conversion produces more characters than this, the field is not truncated.

  Alternatively, if the field width is `*', the next argument in the argument list (before the actual value to be printed) is used as the field width. The width value must be an integer. If the value is negative it is as though the `-' flag is set (see above) and the absolute value is used as the field width.

• An optional precision to specify the number of digits to be written for numeric conversions and the maximum field width for string conversions. The precision is specified by a period (`.') followed optionally by a decimal integer (which defaults to zero if omitted).

  Alternatively, if the precision is `.*', the next argument in the argument list (before the actual value to be printed) is used as the precision. The value must be an integer, and is ignored if negative. If you specify `*' for both the field width and precision, the field width argument precedes the precision argument. The `.*' precision is an enhancement. C library versions may not accept this syntax.

  For the `%f', `%e', and `%E' conversions, the precision specifies how many digits follow the decimal-point character. The default precision is 6. If the precision is explicitly 0, the decimal point character is suppressed.

  For the `%g' and `%G' conversions, the precision specifies how many significant digits to print. Significant digits are the first digit before the decimal point, and all the digits after it. If the precision is 0 or not specified for `%g' or `%G', it is treated like a value of 1. If the value being printed cannot be expressed accurately in the specified number of digits, the value is rounded to the nearest number that fits.

  For exact conversions, if a precision is supplied it specifies the minimum number of digits to appear; leading zeros are produced if necessary. If a precision is not supplied, the number is printed with as many digits as necessary. Converting an exact `0' with an explicit precision of zero produces no characters.

• An optional one of `l', `h' or `L', which is ignored for numeric conversions. It is an error to specify these modifiers for non-numeric conversions.
• A character that specifies the conversion to be applied.

4.3.2.1 Exact Conversions

`b', `B'

Print an integer as an unsigned binary number.

Note: `%b' and `%B' are SLIB extensions.

`d', `i'

Print an integer as a signed decimal number. `%d' and `%i' are synonymous for output, but are different when used with scanf for input (see section Standard Formatted Input).

`o'

Print an integer as an unsigned octal number.

`u'

Print an integer as an unsigned decimal number.

`x', `X'

Print an integer as an unsigned hexadecimal number. `%x' prints using the digits `0123456789abcdef'. `%X' prints using the digits `0123456789ABCDEF'.

4.3.2.2 Inexact Conversions

`f'

Print a floating-point number in fixed-point notation.

`e', `E'

Print a floating-point number in exponential notation. `%e' prints `e' between mantissa and exponont. `%E' prints `E' between mantissa and exponont.

`g', `G'

Print a floating-point number in either fixed or exponential notation, whichever is more appropriate for its magnitude. Unless an `#' flag has been supplied, trailing zeros after a decimal point will be stripped off. `%g' prints `e' between mantissa and exponont. `%G' prints `E' between mantissa and exponent.

`k', `K'

Print a number like `%g', except that an SI prefix is output after the number, which is scaled accordingly. `%K' outputs a space between number and prefix, `%k' does not.

4.3.2.3 Other Conversions

`c'

Print a single character. The `-' flag is the only one which can be specified. It is an error to specify a precision.

`s'

Print a string. The `-' flag is the only one which can be specified. A precision specifies the maximum number of characters to output; otherwise all characters in the string are output.

`a', `A'

Print a scheme expression. The `-' flag left-justifies the output. The `#' flag specifies that strings and characters should be quoted as by write (which can be read using read); otherwise, output is as display prints. A precision specifies the maximum number of characters to output; otherwise as many characters as needed are output.

Note: `%a' and `%A' are SLIB extensions.

`%'

Print a literal `%' character. No argument is consumed. It is an error to specify flags, field width, precision, or type modifiers with `%%'.

4.3.3 Standard Formatted Input

(require 'scanf)

Function: scanf-read-list format

Function: scanf-read-list format port

Function: scanf-read-list format string

Macro: scanf format arg1 …

Macro: fscanf port format arg1 …

Macro: sscanf str format arg1 …

Each function reads characters, interpreting them according to the control string format argument.

scanf-read-list returns a list of the items specified as far as the input matches format. scanf, fscanf, and sscanf return the number of items successfully matched and stored. scanf, fscanf, and sscanf also set the location corresponding to arg1 … using the methods:

symbol

set!

car expression

set-car!

cdr expression

set-cdr!

vector-ref expression

vector-set!

substring expression

substring-move-left!

The argument to a substring expression in arg1 … must be a non-constant string. Characters will be stored starting at the position specified by the second argument to substring. The number of characters stored will be limited by either the position specified by the third argument to substring or the length of the matched string, whichever is less.

The control string, format, contains conversion specifications and other characters used to direct interpretation of input sequences. The control string contains:

• White-space characters (blanks, tabs, newlines, or formfeeds) that cause input to be read (and discarded) up to the next non-white-space character.
• An ordinary character (not `%') that must match the next character of the input stream.
• Conversion specifications, consisting of the character `%', an optional assignment suppressing character `*', an optional numerical maximum-field width, an optional `l', `h' or `L' which is ignored, and a conversion code.

Unless the specification contains the `n' conversion character (described below), a conversion specification directs the conversion of the next input field. The result of a conversion specification is returned in the position of the corresponding argument points, unless `*' indicates assignment suppression. Assignment suppression provides a way to describe an input field to be skipped. An input field is defined as a string of characters; it extends to the next inappropriate character or until the field width, if specified, is exhausted.

Note: This specification of format strings differs from the ANSI C and POSIX specifications. In SLIB, white space before an input field is not skipped unless white space appears before the conversion specification in the format string. In order to write format strings which work identically with ANSI C and SLIB, prepend whitespace to all conversion specifications except `[' and `c'.

The conversion code indicates the interpretation of the input field; For a suppressed field, no value is returned. The following conversion codes are legal:

`%'

A single % is expected in the input at this point; no value is returned.

`d', `D'

A decimal integer is expected.

`u', `U'

An unsigned decimal integer is expected.

`o', `O'

An octal integer is expected.

`x', `X'

A hexadecimal integer is expected.

`i'

An integer is expected. Returns the value of the next input item, interpreted according to C conventions; a leading `0' implies octal, a leading `0x' implies hexadecimal; otherwise, decimal is assumed.

`n'

Returns the total number of bytes (including white space) read by scanf. No input is consumed by %n.

`f', `F', `e', `E', `g', `G'

A floating-point number is expected. The input format for floating-point numbers is an optionally signed string of digits, possibly containing a radix character `.', followed by an optional exponent field consisting of an `E' or an `e', followed by an optional `+', `-', or space, followed by an integer.

`c', `C'

Width characters are expected. The normal skip-over-white-space is suppressed in this case; to read the next non-space character, use `%1s'. If a field width is given, a string is returned; up to the indicated number of characters is read.

`s', `S'

A character string is expected The input field is terminated by a white-space character. scanf cannot read a null string.

`['

Indicates string data and the normal skip-over-leading-white-space is suppressed. The left bracket is followed by a set of characters, called the scanset, and a right bracket; the input field is the maximal sequence of input characters consisting entirely of characters in the scanset. `^', when it appears as the first character in the scanset, serves as a complement operator and redefines the scanset as the set of all characters not contained in the remainder of the scanset string. Construction of the scanset follows certain conventions. A range of characters may be represented by the construct first-last, enabling `[0123456789]' to be expressed `[0-9]'. Using this convention, first must be lexically less than or equal to last; otherwise, the dash stands for itself. The dash also stands for itself when it is the first or the last character in the scanset. To include the right square bracket as an element of the scanset, it must appear as the first character (possibly preceded by a `^') of the scanset, in which case it will not be interpreted syntactically as the closing bracket. At least one character must match for this conversion to succeed.

The scanf functions terminate their conversions at end-of-file, at the end of the control string, or when an input character conflicts with the control string. In the latter case, the offending character is left unread in the input stream.

4.4 Program and Arguments

4.4.1 Getopt

(require 'getopt)

This routine implements Posix command line argument parsing. Notice that returning values through global variables means that getopt is not reentrant.

Obedience to Posix format for the getopt calls sows confusion. Passing argc and argv as arguments while referencing optind as a global variable leads to strange behavior, especially when the calls to getopt are buried in other procedures.

Even in C, argc can be derived from argv; what purpose does it serve beyond providing an opportunity for argv/argc mismatch? Just such a mismatch existed for years in a SLIB getopt-- example.

I have removed the argc and argv arguments to getopt procedures; and replaced them with a global variable:

Variable: *argv*

Define *argv* with a list of arguments before calling getopt procedures. If you don't want the first (0th) element to be ignored, set *optind* to 0 (after requiring getopt).

Variable: *optind*

Is the index of the current element of the command line. It is initially one. In order to parse a new command line or reparse an old one, *optind* must be reset.

Variable: *optarg*

Is set by getopt to the (string) option-argument of the current option.

Function: getopt optstring

Returns the next option letter in *argv* (starting from (vector-ref argv *optind*)) that matches a letter in optstring. *argv* is a vector or list of strings, the 0th of which getopt usually ignores. optstring is a string of recognized option characters; if a character is followed by a colon, the option takes an argument which may be immediately following it in the string or in the next element of *argv*.

*optind* is the index of the next element of the *argv* vector to be processed. It is initialized to 1 by `getopt.scm', and getopt updates it when it finishes with each element of *argv*.

getopt returns the next option character from *argv* that matches a character in optstring, if there is one that matches. If the option takes an argument, getopt sets the variable *optarg* to the option-argument as follows:

• If the option was the last character in the string pointed to by an element of *argv*, then *optarg* contains the next element of *argv*, and *optind* is incremented by 2. If the resulting value of *optind* is greater than or equal to (length *argv*), this indicates a missing option argument, and getopt returns an error indication.
• Otherwise, *optarg* is set to the string following the option character in that element of *argv*, and *optind* is incremented by 1.

If, when getopt is called, the string (vector-ref argv *optind*) either does not begin with the character #\- or is just "-", getopt returns #f without changing *optind*. If (vector-ref argv *optind*) is the string "--", getopt returns #f after incrementing *optind*.

If getopt encounters an option character that is not contained in optstring, it returns the question-mark #\? character. If it detects a missing option argument, it returns the colon character #\: if the first character of optstring was a colon, or a question-mark character otherwise. In either case, getopt sets the variable getopt:opt to the option character that caused the error.

The special option "--" can be used to delimit the end of the options; #f is returned, and "--" is skipped.

RETURN VALUE

getopt returns the next option character specified on the command line. A colon #\: is returned if getopt detects a missing argument and the first character of optstring was a colon #\:.

A question-mark #\? is returned if getopt encounters an option character not in optstring or detects a missing argument and the first character of optstring was not a colon #\:.

Otherwise, getopt returns #f when all command line options have been parsed.

Example:

#! /usr/bin/scm ;;;This code is SCM specific. (define argv (program-arguments)) (require 'getopt) (define opts ":a:b:cd") (let loop ((opt (getopt (length argv) argv opts))) (case opt ((#\a) (print "option a: " *optarg*)) ((#\b) (print "option b: " *optarg*)) ((#\c) (print "option c")) ((#\d) (print "option d")) ((#\?) (print "error" getopt:opt)) ((#\:) (print "missing arg" getopt:opt)) ((#f) (if (< *optind* (length argv)) (print "argv[" *optind* "]=" (list-ref argv *optind*))) (set! *optind* (+ *optind* 1)))) (if (< *optind* (length argv)) (loop (getopt (length argv) argv opts)))) (slib:exit)

4.4.2 Getopt--

Function: getopt-- optstring

The procedure getopt-- is an extended version of getopt which parses long option names of the form `--hold-the-onions' and `--verbosity-level=extreme'. Getopt-- behaves as getopt except for non-empty options beginning with `--'.

Options beginning with `--' are returned as strings rather than characters. If a value is assigned (using `=') to a long option, *optarg* is set to the value. The `=' and value are not returned as part of the option string.

No information is passed to getopt-- concerning which long options should be accepted or whether such options can take arguments. If a long option did not have an argument, *optarg* will be set to #f. The caller is responsible for detecting and reporting errors.

(define opts ":-:b:") (define *argv* '("foo" "-b9" "--f1" "--2=" "--g3=35234.342" "--")) (define *optind* 1) (define *optarg* #f) (require 'qp) (do ((i 5 (+ -1 i))) ((zero? i)) (let ((opt (getopt-- opts))) (print *optind* opt *optarg*))) -| 2 #\b "9" 3 "f1" #f 4 "2" "" 5 "g3" "35234.342" 5 #f "35234.342"

4.4.3 Command Line

(require 'read-command)

Function: read-command port

Function: read-command

read-command converts a command line into a list of strings suitable for parsing by getopt. The syntax of command lines supported resembles that of popular shells. read-command updates port to point to the first character past the command delimiter.

If an end of file is encountered in the input before any characters are found that can begin an object or comment, then an end of file object is returned.

The port argument may be omitted, in which case it defaults to the value returned by current-input-port.

The fields into which the command line is split are delimited by whitespace as defined by char-whitespace?. The end of a command is delimited by end-of-file or unescaped semicolon (;) or newline. Any character can be literally included in a field by escaping it with a backslach (\).

The initial character and types of fields recognized are:

`\'

The next character has is taken literally and not interpreted as a field delimiter. If \ is the last character before a newline, that newline is just ignored. Processing continues from the characters after the newline as though the backslash and newline were not there.

`"'

The characters up to the next unescaped " are taken literally, according to [R4RS] rules for literal strings (see (r4rs)Strings section `Strings' in Revised(4) Scheme).

`(', `%''

One scheme expression is read starting with this character. The read expression is evaluated, converted to a string (using display), and replaces the expression in the returned field.

`;'

Semicolon delimits a command. Using semicolons more than one command can appear on a line. Escaped semicolons and semicolons inside strings do not delimit commands.

The comment field differs from the previous fields in that it must be the first character of a command or appear after whitespace in order to be recognized. # can be part of fields if these conditions are not met. For instance, ab#c is just the field ab#c.

`#'

Introduces a comment. The comment continues to the end of the line on which the semicolon appears. Comments are treated as whitespace by read-dommand-line and backslashes before newlines in comments are also ignored.

Function: read-options-file filename

read-options-file converts an options file into a list of strings suitable for parsing by getopt. The syntax of options files is the same as the syntax for command lines, except that newlines do not terminate reading (only ; or end of file).

If an end of file is encountered before any characters are found that can begin an object or comment, then an end of file object is returned.

4.4.4 Parameter lists

(require 'parameters)

Arguments to procedures in scheme are distinguished from each other by their position in the procedure call. This can be confusing when a procedure takes many arguments, many of which are not often used.

A parameter-list is a way of passing named information to a procedure. Procedures are also defined to set unused parameters to default values, check parameters, and combine parameter lists.

A parameter has the form (parameter-name value1 …). This format allows for more than one value per parameter-name.

A parameter-list is a list of parameters, each with a different parameter-name.

Function: make-parameter-list parameter-names

Returns an empty parameter-list with slots for parameter-names.

Function: parameter-list-ref parameter-list parameter-name

parameter-name must name a valid slot of parameter-list. parameter-list-ref returns the value of parameter parameter-name of parameter-list.

Function: remove-parameter parameter-name parameter-list

Removes the parameter parameter-name from parameter-list. remove-parameter does not alter the argument parameter-list.

If there are more than one parameter-name parameters, an error is signaled.

Procedure: adjoin-parameters! parameter-list parameter1 …

Returns parameter-list with parameter1 … merged in.

Procedure: parameter-list-expand expanders parameter-list

expanders is a list of procedures whose order matches the order of the parameter-names in the call to make-parameter-list which created parameter-list. For each non-false element of expanders that procedure is mapped over the corresponding parameter value and the returned parameter lists are merged into parameter-list.

This process is repeated until parameter-list stops growing. The value returned from parameter-list-expand is unspecified.

Function: fill-empty-parameters defaulters parameter-list

defaulters is a list of procedures whose order matches the order of the parameter-names in the call to make-parameter-list which created parameter-list. fill-empty-parameters returns a new parameter-list with each empty parameter replaced with the list returned by calling the corresponding defaulter with parameter-list as its argument.

Function: check-parameters checks parameter-list

checks is a list of procedures whose order matches the order of the parameter-names in the call to make-parameter-list which created parameter-list.

check-parameters returns parameter-list if each check of the corresponding parameter-list returns non-false. If some check returns #f a warning is signaled.

In the following procedures arities is a list of symbols. The elements of arities can be:

single

Requires a single parameter.

optional

A single parameter or no parameter is acceptable.

boolean

A single boolean parameter or zero parameters is acceptable.

nary

Any number of parameters are acceptable.

nary1

One or more of parameters are acceptable.

Function: parameter-list->arglist positions arities parameter-list

Returns parameter-list converted to an argument list. Parameters of arity type single and boolean are converted to the single value associated with them. The other arity types are converted to lists of the value(s).

positions is a list of positive integers whose order matches the order of the parameter-names in the call to make-parameter-list which created parameter-list. The integers specify in which argument position the corresponding parameter should appear.

4.4.5 Getopt Parameter lists

(require 'getopt-parameters)

Function: getopt->parameter-list optnames arities types aliases desc …

Returns *argv* converted to a parameter-list. optnames are the parameter-names. arities and types are lists of symbols corresponding to optnames.

aliases is a list of lists of strings or integers paired with elements of optnames. Each one-character string will be treated as a single `-' option by getopt. Longer strings will be treated as long-named options (see section getopt-).

If the aliases association list has only strings as its cars, then all the option-arguments after an option (and before the next option) are adjoined to that option.

If the aliases association list has integers, then each (string) option will take at most one option-argument. Unoptioned arguments are collected in a list. A `-1' alias will take the last argument in this list; `+1' will take the first argument in the list. The aliases -2 then +2; -3 then +3; … are tried so long as a positive or negative consecutive alias is found and arguments remain in the list. Finally a `0' alias, if found, absorbs any remaining arguments.

In all cases, if unclaimed arguments remain after processing, a warning is signaled and #f is returned.

Function: getopt->arglist optnames positions arities types defaulters checks aliases desc …

Like getopt->parameter-list, but converts *argv* to an argument-list as specified by optnames, positions, arities, types, defaulters, checks, and aliases. If the options supplied violate the arities or checks constraints, then a warning is signaled and #f is returned.

These getopt functions can be used with SLIB relational databases. For an example, See section make-command-server.

If errors are encountered while processing options, directions for using the options (and argument strings desc …) are printed to current-error-port.

(begin
  (set! *optind* 1)
  (set! *argv* '("cmd" "-?")
  (getopt->parameter-list
   '(flag number symbols symbols string flag2 flag3 num2 num3)
   '(boolean optional nary1 nary single boolean boolean nary nary)
   '(boolean integer symbol symbol string boolean boolean integer integer)
   '(("flag" flag)
     ("f" flag)
     ("Flag" flag2)
     ("B" flag3)
     ("optional" number)
     ("o" number)
     ("nary1" symbols)
     ("N" symbols)
     ("nary" symbols)
     ("n" symbols)
     ("single" string)
     ("s" string)
     ("a" num2)
     ("Abs" num3))))
-|
Usage: cmd [OPTION ARGUMENT ...] ...

  -f, --flag
  -o, --optional=<number>
  -n, --nary=<symbols> ...
  -N, --nary1=<symbols> ...
  -s, --single=<string>
      --Flag
  -B
  -a        <num2> ...
      --Abs=<num3> ...

ERROR: getopt->parameter-list "unrecognized option" "-?"

4.4.6 Filenames

(require 'filename) or (require 'glob)

Function: filename:match?? pattern

Function: filename:match-ci?? pattern

Returns a predicate which returns a non-false value if its string argument matches (the string) pattern, false otherwise. Filename matching is like glob expansion described the bash manpage, except that names beginning with `.' are matched and `/' characters are not treated specially.

These functions interpret the following characters specially in pattern strings:

`*'

Matches any string, including the null string.

`?'

Matches any single character.

`[…]'

Matches any one of the enclosed characters. A pair of characters separated by a minus sign (-) denotes a range; any character lexically between those two characters, inclusive, is matched. If the first character following the `[' is a `!' or a `^' then any character not enclosed is matched. A `-' or `]' may be matched by including it as the first or last character in the set.

Function: filename:substitute?? pattern template

Function: filename:substitute-ci?? pattern template

Returns a function transforming a single string argument according to glob patterns pattern and template. pattern and template must have the same number of wildcard specifications, which need not be identical. pattern and template may have a different number of literal sections. If an argument to the function matches pattern in the sense of filename:match?? then it returns a copy of template in which each wildcard specification is replaced by the part of the argument matched by the corresponding wildcard specification in pattern. A * wildcard matches the longest leftmost string possible. If the argument does not match pattern then false is returned.

template may be a function accepting the same number of string arguments as there are wildcard specifications in pattern. In the case of a match the result of applying template to a list of the substrings matched by wildcard specifications will be returned, otherwise template will not be called and #f will be returned.

((filename:substitute?? "scm_[0-9]*.html" "scm5c4_??.htm")
 "scm_10.html")
⇒ "scm5c4_10.htm"
((filename:substitute?? "??" "beg?mid?end") "AZ")
⇒ "begAmidZend"
((filename:substitute?? "*na*" "?NA?") "banana")
⇒ "banaNA"
((filename:substitute?? "?*?" (lambda (s1 s2 s3) (string-append s3 s1)))
 "ABZ")
⇒ "ZA"

Function: replace-suffix str old new

str can be a string or a list of strings. Returns a new string (or strings) similar to str but with the suffix string old removed and the suffix string new appended. If the end of str does not match old, an error is signaled.

(replace-suffix "/usr/share/slib/batch.scm" ".scm" ".c")
⇒ "/usr/share/slib/batch.c"

Function: call-with-tmpnam proc k

Function: call-with-tmpnam proc

Calls proc with k arguments, strings returned by successive calls to tmpnam. If proc returns, then any files named by the arguments to proc are deleted automatically and the value(s) yielded by the proc is(are) returned. k may be ommited, in which case it defaults to 1.

Function: call-with-tmpnam proc suffix1 …

Calls proc with strings returned by successive calls to tmpnam, each with the corresponding suffix string appended. If proc returns, then any files named by the arguments to proc are deleted automatically and the value(s) yielded by the proc is(are) returned.

4.4.7 Batch

(require 'batch)

The batch procedures provide a way to write and execute portable scripts for a variety of operating systems. Each batch: procedure takes as its first argument a parameter-list (see section Parameter lists). This parameter-list argument parms contains named associations. Batch currently uses 2 of these:

batch-port

The port on which to write lines of the batch file.

batch-dialect

The syntax of batch file to generate. Currently supported are:

• unix
• dos
• vms
• amigaos
• system
• *unknown*

`batch.scm' uses 2 enhanced relational tables (see section Using Databases) to store information linking the names of operating-systems to batch-dialectes.

Function: batch:initialize! database

Defines operating-system and batch-dialect tables and adds the domain operating-system to the enhanced relational database database.

Variable: *operating-system*

Is batch's best guess as to which operating-system it is running under. *operating-system* is set to (software-type) (see section Configuration) unless (software-type) is unix, in which case finer distinctions are made.

Function: batch:call-with-output-script parms file proc

proc should be a procedure of one argument. If file is an output-port, batch:call-with-output-script writes an appropriate header to file and then calls proc with file as the only argument. If file is a string, batch:call-with-output-script opens a output-file of name file, writes an appropriate header to file, and then calls proc with the newly opened port as the only argument. Otherwise, batch:call-with-output-script acts as if it was called with the result of (current-output-port) as its third argument.

The rest of the batch: procedures write (or execute if batch-dialect is system) commands to the batch port which has been added to parms or (copy-tree parms) by the code:

(adjoin-parameters! parms (list 'batch-port port))

Function: batch:command parms string1 string2 …

Calls batch:try-command (below) with arguments, but signals an error if batch:try-command returns #f.

These functions return a non-false value if the command was successfully translated into the batch dialect and #f if not. In the case of the system dialect, the value is non-false if the operation suceeded.

Function: batch:try-command parms string1 string2 …

Writes a command to the batch-port in parms which executes the program named string1 with arguments string2 ….

Function: batch:try-chopped-command parms arg1 arg2 … list

breaks the last argument list into chunks small enough so that the command:

arg1 arg2 … chunk

fits withing the platform's maximum command-line length.

batch:try-chopped-command calls batch:try-command with the command and returns non-false only if the commands all fit and batch:try-command of each command line returned non-false.

Function: batch:run-script parms string1 string2 …

Writes a command to the batch-port in parms which executes the batch script named string1 with arguments string2 ….

Note: batch:run-script and batch:try-command are not the same for some operating systems (VMS).

Function: batch:comment parms line1 …

Writes comment lines line1 … to the batch-port in parms.

Function: batch:lines->file parms file line1 …

Writes commands to the batch-port in parms which create a file named file with contents line1 ….

Function: batch:delete-file parms file

Writes a command to the batch-port in parms which deletes the file named file.

Function: batch:rename-file parms old-name new-name

Writes a command to the batch-port in parms which renames the file old-name to new-name.

In addition, batch provides some small utilities very useful for writing scripts:

Function: truncate-up-to path char

Function: truncate-up-to path string

Function: truncate-up-to path charlist

path can be a string or a list of strings. Returns path sans any prefixes ending with a character of the second argument. This can be used to derive a filename moved locally from elsewhere.

(truncate-up-to "/usr/share/slib/batch.scm" "/") ⇒ "batch.scm"

Function: string-join joiner string1 …

Returns a new string consisting of all the strings string1 … in order appended together with the string joiner between each adjacent pair.

Function: must-be-first list1 list2

Returns a new list consisting of the elements of list2 ordered so that if some elements of list1 are equal? to elements of list2, then those elements will appear first and in the order of list1.

Function: must-be-last list1 list2

Returns a new list consisting of the elements of list1 ordered so that if some elements of list2 are equal? to elements of list1, then those elements will appear last and in the order of list2.

Function: os->batch-dialect osname

Returns its best guess for the batch-dialect to be used for the operating-system named osname. os->batch-dialect uses the tables added to database by batch:initialize!.

Here is an example of the use of most of batch's procedures:

(require 'databases)
(require 'parameters)
(require 'batch)
(require 'glob)

(define batch (create-database #f 'alist-table))
(batch:initialize! batch)

(define my-parameters
  (list (list 'batch-dialect (os->batch-dialect *operating-system*))
        (list 'operating-system *operating-system*)
        (list 'batch-port (current-output-port)))) ;gets filled in later

(batch:call-with-output-script
 my-parameters
 "my-batch"
 (lambda (batch-port)
   (adjoin-parameters! my-parameters (list 'batch-port batch-port))
   (and
    (batch:comment my-parameters
                   "================ Write file with C program.")
    (batch:rename-file my-parameters "hello.c" "hello.c~")
    (batch:lines->file my-parameters "hello.c"
                       "#include <stdio.h>"
                       "int main(int argc, char **argv)"
                       "{"
                       "  printf(\"hello world\\n\");"
                       "  return 0;"
                       "}" )
    (batch:command my-parameters "cc" "-c" "hello.c")
    (batch:command my-parameters "cc" "-o" "hello"
                  (replace-suffix "hello.c" ".c" ".o"))
    (batch:command my-parameters "hello")
    (batch:delete-file my-parameters "hello")
    (batch:delete-file my-parameters "hello.c")
    (batch:delete-file my-parameters "hello.o")
    (batch:delete-file my-parameters "my-batch")
    )))

Produces the file `my-batch':

#! /bin/sh
# "my-batch" script created by SLIB/batch Sun Oct 31 18:24:10 1999
# ================ Write file with C program.
mv -f hello.c hello.c~
rm -f hello.c
echo '#include <stdio.h>'>>hello.c
echo 'int main(int argc, char **argv)'>>hello.c
echo '{'>>hello.c
echo '  printf("hello world\n");'>>hello.c
echo '  return 0;'>>hello.c
echo '}'>>hello.c
cc -c hello.c
cc -o hello hello.o
hello
rm -f hello
rm -f hello.c
rm -f hello.o
rm -f my-batch

When run, `my-batch' prints:

bash$ my-batch
mv: hello.c: No such file or directory
hello world

4.5 HTML

(require 'html-form)

Function: html:atval txt

Returns a string with character substitutions appropriate to send txt as an attribute-value.

Function: html:plain txt

Returns a string with character substitutions appropriate to send txt as an plain-text.

Function: html:meta name content

Returns a tag of meta-information suitable for passing as the third argument to html:head. The tag produced is `<META NAME="name" CONTENT="content">'. The string or symbol name can be `author', `copyright', `keywords', `description', `date', `robots', ….

Function: html:http-equiv name content

Returns a tag of HTTP information suitable for passing as the third argument to html:head. The tag produced is `<META HTTP-EQUIV="name" CONTENT="content">'. The string or symbol name can be `Expires', `PICS-Label', `Content-Type', `Refresh', ….

Function: html:meta-refresh delay uri

Function: html:meta-refresh delay

Returns a tag suitable for passing as the third argument to html:head. If uri argument is supplied, then delay seconds after displaying the page with this tag, Netscape or IE browsers will fetch and display uri. Otherwise, delay seconds after displaying the page with this tag, Netscape or IE browsers will fetch and redisplay this page.

Function: html:head title backlink tags …

Function: html:head title backlink

Function: html:head title

Returns header string for an HTML page named title. If backlink is a string, it is used verbatim between the `H1' tags; otherwise title is used. If string arguments tags ... are supplied, then they are included verbatim within the <HEAD> section.

Function: html:body body …

Returns HTML string to end a page.

Function: html:pre line1 line …

Returns the strings line1, lines as PREformmated plain text (rendered in fixed-width font). Newlines are inserted between line1, lines. HTML tags (`<tag>') within lines will be visible verbatim.

Function: html:comment line1 line …

Returns the strings line1 as HTML comments.

4.6 HTML Forms

Function: html:form method action body …

The symbol method is either get, head, post, put, or delete. The strings body form the body of the form. html:form returns the HTML form.

Function: html:hidden name value

Returns HTML string which will cause name=value in form.

Function: html:checkbox pname default

Returns HTML string for check box.

Function: html:text pname default size …

Returns HTML string for one-line text box.

Function: html:text-area pname default-list

Returns HTML string for multi-line text box.

Function: html:select pname arity default-list foreign-values

Returns HTML string for pull-down menu selector.

Function: html:buttons pname arity default-list foreign-values

Returns HTML string for any-of selector.

Function: form:submit submit-label command

Function: form:submit submit-label

The string or symbol submit-label appears on the button which submits the form. If the optional second argument command is given, then *command*=command and *button*=submit-label are set in the query. Otherwise, *command*=submit-label is set in the query.

Function: form:image submit-label image-src

The image-src appears on the button which submits the form.

Function: form:reset

Returns a string which generates a reset button.

Function: form:element pname arity default-list foreign-values

Returns a string which generates an INPUT element for the field named pname. The element appears in the created form with its representation determined by its arity and domain. For domains which are foreign-keys:

single

select menu

optional

select menu

nary

check boxes

nary1

check boxes

If the foreign-key table has a field named `visible-name', then the contents of that field are the names visible to the user for those choices. Otherwise, the foreign-key itself is visible.

For other types of domains:

single

text area

optional

text area

boolean

check box

nary

text area

nary1

text area

Function: form:delimited pname doc aliat arity default-list foreign-values

Returns a HTML string for a form element embedded in a line of a delimited list. Apply map form:delimited to the list returned by command->p-specs.

Function: html:delimited-list row …

Wraps its arguments with delimited-list (`DL' command.

Function: get-foreign-choices tab

Returns a list of the `visible-name' or first fields of table tab.

Function: command->p-specs rdb command-table command

The symbol command-table names a command table in the rdb relational database. The symbol command names a key in command-table.

command->p-specs returns a list of lists of pname, doc, aliat, arity, default-list, and foreign-values. The returned list has one element for each parameter of command command.

This example demonstrates how to create a HTML-form for the `build' command.

(require (in-vicinity (implementation-vicinity) "build.scm")) (call-with-output-file "buildscm.html" (lambda (port) (display (string-append (html:head 'commands) (html:body (sprintf #f "<H2>%s:</H2><BLOCKQUOTE>%s</BLOCKQUOTE>\\n" (html:plain 'build) (html:plain ((comtab 'get 'documentation) 'build))) (html:form 'post (or "http://localhost:8081/buildscm" "/cgi-bin/build.cgi") (apply html:delimited-list (apply map form:delimited (command->p-specs build '*commands* 'build))) (form:submit 'build) (form:reset)))) port)))

4.7 HTML Tables

(require 'db->html)

Function: html:table options row …

Function: html:caption caption align

Function: html:caption caption

align can be `top' or `bottom'.

Function: html:heading columns

Outputs a heading row for the currently-started table.

Function: html:href-heading columns uris

Outputs a heading row with column-names columns linked to URIs uris.

Function: html:linked-row-converter k foreigns

The positive integer k is the primary-key-limit (number of primary-keys) of the table. foreigns is a list of the filenames of foreign-key field pages and #f for non foreign-key fields.

html:linked-row-converter returns a procedure taking a row for its single argument. This returned procedure returns the html string for that table row.

Function: table-name->filename table-name

Returns the symbol table-name converted to a filename.

Function: table->linked-html caption db table-name match-key1 …

Returns HTML string for db table table-name. Every foreign-key value is linked to the page (of the table) defining that key.

The optional match-key1 … arguments restrict actions to a subset of the table. See section match-key.

Function: table->linked-page db table-name index-filename arg …

Returns a complete HTML page. The string index-filename names the page which refers to this one.

The optional args … arguments restrict actions to a subset of the table. See section match-key.

Function: catalog->html db caption arg …

Returns HTML string for the catalog table of db.

4.7.1 HTML editing tables

A client can modify one row of an editable table at a time. For any change submitted, these routines check if that row has been modified during the time the user has been editing the form. If so, an error page results.

The behavior of edited rows is:

• If no fields are changed, then no change is made to the table.
• If the primary keys equal null-keys (parameter defaults), and no other user has modified that row, then that row is deleted.
• If only primary keys are changed, there are non-key fields, and no row with the new keys is in the table, then the old row is deleted and one with the new keys is inserted.
• If only non-key fields are changed, and that row has not been modified by another user, then the row is changed to reflect the fields.
• If both keys and non-key fields are changed, and no row with the new keys is in the table, then a row is created with the new keys and fields.
• If fields are changed, all fields are primary keys, and no row with the new keys is in the table, then a row is created with the new keys.

After any change to the table, a sync-database of the database is performed.

Function: command:modify-table table-name null-keys update delete retrieve

Function: command:modify-table table-name null-keys update delete

Function: command:modify-table table-name null-keys update

Function: command:modify-table table-name null-keys

Returns procedure (of db) which returns procedure to modify row of table-name. null-keys is the list of null keys indicating the row is to be deleted when any matches its corresponding primary key. Optional arguments update, delete, and retrieve default to the row:update, row:delete, and row:retrieve of table-name in db.

Function: command:make-editable-table rdb table-name arg …

Given table-name in rdb, creates parameter and *command* tables for editing one row of table-name at a time. command:make-editable-table returns a procedure taking a row argument which returns the HTML string for editing that row.

Optional args are expressions (lists) added to the call to command:modify-table.

The domain name of a column determines the expected arity of the data stored in that column. Domain names ending in:

`*'

have arity `nary';

`+'

have arity `nary1'.

Function: html:editable-row-converter k names edit-point edit-converter

The positive integer k is the primary-key-limit (number of primary-keys) of the table. names is a list of the field-names. edit-point is the list of primary-keys denoting the row to edit (or #f). edit-converter is the procedure called with k, names, and the row to edit.

html:editable-row-converter returns a procedure taking a row for its single argument. This returned procedure returns the html string for that table row.

Each HTML table constructed using html:editable-row-converter has first k fields (typically the primary key fields) of each row linked to a text encoding of these fields (the result of calling row->anchor). The page so referenced typically allows the user to edit fields of that row.

4.7.2 HTML databases

Function: db->html-files db dir index-filename caption

db must be a relational database. dir must be #f or a non-empty string naming an existing sub-directory of the current directory.

db->html-files creates an html page for each table in the database db in the sub-directory named dir, or the current directory if dir is #f. The top level page with the catalog of tables (captioned caption) is written to a file named index-filename.

Function: db->html-directory db dir index-filename

Function: db->html-directory db dir

db must be a relational database. dir must be a non-empty string naming an existing sub-directory of the current directory or one to be created. The optional string index-filename names the filename of the top page, which defaults to `index.html'.

db->html-directory creates sub-directory dir if neccessary, and calls (db->html-files db dir index-filename dir). The `file:' URI of index-filename is returned.

Function: db->netscape db dir index-filename

Function: db->netscape db dir

db->netscape is just like db->html-directory, but calls browse-url with the uri for the top page after the pages are created.

4.8 HTTP and CGI

(require 'http) or (require 'cgi)

Function: http:header alist

Returns a string containing lines for each element of alist; the car of which is followed by `: ', then the cdr.

Function: http:content alist body …

Returns the concatenation of strings body with the (http:header alist) and the `Content-Length' prepended.

Variable: *http:byline*

String appearing at the bottom of error pages.

Function: http:error-page status-code reason-phrase html-string …

status-code and reason-phrase should be an integer and string as specified in RFC 2068. The returned page (string) will show the status-code and reason-phrase and any additional html-strings …; with *http:byline* or SLIB's default at the bottom.

Function: http:forwarding-page title delay uri html-string …

The string or symbol title is the page title. delay is a non-negative integer. The html-strings … are typically used to explain to the user why this page is being forwarded.

http:forwarding-page returns an HTML string for a page which automatically forwards to uri after delay seconds. The returned page (string) contains any html-strings … followed by a manual link to uri, in case the browser does not forward automatically.

Function: http:serve-query serve-proc input-port output-port

reads the URI and query-string from input-port. If the query is a valid `"POST"' or `"GET"' query, then http:serve-query calls serve-proc with three arguments, the request-line, query-string, and header-alist. Otherwise, http:serve-query calls serve-proc with the request-line, #f, and header-alist.

If serve-proc returns a string, it is sent to output-port. If serve-proc returns a list, then an error page with number 525 and strings from the list. If serve-proc returns #f, then a `Bad Request' (400) page is sent to output-port.

Otherwise, http:serve-query replies (to output-port) with appropriate HTML describing the problem.

This example services HTTP queries from port-number:

(define socket (make-stream-socket AF_INET 0))
(and (socket:bind socket port-number) ; AF_INET INADDR_ANY
     (socket:listen socket 10)        ; Queue up to 10 requests.
     (dynamic-wind
         (lambda () #f)
         (lambda ()
           (do ((port (socket:accept socket) (socket:accept socket)))
               (#f)
             (let ((iport (duplicate-port port "r"))
                   (oport (duplicate-port port "w")))
               (http:serve-query build:serve iport oport)
               (close-port iport)
               (close-port oport))
             (close-port port)))
         (lambda () (close-port socket))))

Function: cgi:serve-query serve-proc

reads the URI and query-string from (current-input-port). If the query is a valid `"POST"' or `"GET"' query, then cgi:serve-query calls serve-proc with three arguments, the request-line, query-string, and header-alist. Otherwise, cgi:serve-query calls serve-proc with the request-line, #f, and header-alist.

If serve-proc returns a string, it is sent to (current-input-port). If serve-proc returns a list, then an error page with number 525 and strings from the list. If serve-proc returns #f, then a `Bad Request' (400) page is sent to (current-input-port).

Otherwise, cgi:serve-query replies (to (current-input-port)) with appropriate HTML describing the problem.

Function: make-query-alist-command-server rdb command-table

Function: make-query-alist-command-server rdb command-table #t

Returns a procedure of one argument. When that procedure is called with a query-alist (as returned by uri:decode-query, the value of the `*command*' association will be the command invoked in command-table. If `*command*' is not in the query-alist then the value of `*suggest*' is tried. If neither name is in the query-alist, then the literal value `*default*' is tried in command-table.

If optional third argument is non-false, then the command is called with just the parameter-list; otherwise, command is called with the arguments described in its table.

4.9 Parsing HTML

(require 'html-for-each)

Function: html-for-each file word-proc markup-proc white-proc newline-proc

file is an input port or a string naming an existing file containing HTML text. word-proc is a procedure of one argument or #f. markup-proc is a procedure of one argument or #f. white-proc is a procedure of one argument or #f. newline-proc is a procedure of no arguments or #f.

html-for-each opens and reads characters from port file or the file named by string file. Sequential groups of characters are assembled into strings which are either

• enclosed by `<' and `>' (hypertext markups or comments);
• end-of-line;
• whitespace; or
• none of the above (words).

Procedures are called according to these distinctions in order of the string's occurrence in file.

newline-proc is called with no arguments for end-of-line not within a markup or comment.

white-proc is called with strings of non-newline whitespace.

markup-proc is called with hypertext markup strings (including `<' and `>').

word-proc is called with the remaining strings.

html-for-each returns an unspecified value.

Function: html:read-title file limit

Function: html:read-title file

file is an input port or a string naming an existing file containing HTML text. If supplied, limit must be an integer. limit defaults to 1000.

html:read-title opens and reads HTML from port file or the file named by string file, until reaching the (mandatory) `TITLE' field. html:read-title returns the title string with adjacent whitespaces collapsed to one space. html:read-title returns #f if the title field is empty, absent, if the first character read from file is not `#\<', or if the end of title is not found within the first (approximately) limit words.

Function: htm-fields htm

htm is a hypertext markup string.

If htm is a (hypertext) comment, then htm-fields returns #f. Otherwise htm-fields returns the hypertext element symbol (created by string-ci->symbol) consed onto an association list of the attribute name-symbols and values. Each value is a number or string; or #t if the name had no value assigned within the markup.

4.10 URI

(require 'uri)

Implements Uniform Resource Identifiers (URI) as described in RFC 2396.

Function: make-uri

Function: make-uri fragment

Function: make-uri query fragment

Function: make-uri path query fragment

Function: make-uri authority path query fragment

Function: make-uri scheme authority path query fragment

Returns a Uniform Resource Identifier string from component arguments.

Function: uri:make-path path

Returns a URI string combining the components of list path.

Function: html:anchor name

Returns a string which defines this location in the (HTML) file as name. The hypertext `<A HREF="#name">' will link to this point.

(html:anchor "(section 7)") ⇒ "<A NAME=\"(section%207)\"></A>"

Function: html:link uri highlighted

Returns a string which links the highlighted text to uri.

(html:link (make-uri "(section 7)") "section 7") ⇒ "<A HREF=\"#(section%207)\">section 7</A>"

Function: html:base uri

Returns a string specifying the base uri of a document, for inclusion in the HEAD of the document (see section head).

Function: html:isindex prompt

Returns a string specifying the search prompt of a document, for inclusion in the HEAD of the document (see section head).

Function: uri->tree uri-reference base-tree

Function: uri->tree uri-reference

Returns a list of 5 elements corresponding to the parts (scheme authority path query fragment) of string uri-reference. Elements corresponding to absent parts are #f.

The path is a list of strings. If the first string is empty, then the path is absolute; otherwise relative. The optional base-tree is a tree as returned by uri->tree; and is used as the base address for relative URIs.

If the authority component is a Server-based Naming Authority, then it is a list of the userinfo, host, and port strings (or #f). For other types of authority components the authority will be a string.

(uri->tree "http://www.ics.uci.edu/pub/ietf/uri/#Related") ⇒ (http "www.ics.uci.edu" ("" "pub" "ietf" "uri" "") #f "Related")

Function: uri:split-fields txt chr

Returns a list of txt split at each occurrence of chr. chr does not appear in the returned list of strings.

Function: uri:decode-query query-string

Converts a URI encoded query-string to a query-alist.

uric: prefixes indicate procedures dealing with URI-components.

Function: uric:encode uri-component allows

Returns a copy of the string uri-component in which all unsafe octets (as defined in RFC 2396) have been `%' escaped. uric:decode decodes strings encoded by uric:encode.

Function: uric:decode uri-component

Returns a copy of the string uri-component in which each `%' escaped characters in uri-component is replaced with the character it encodes. This routine is useful for showing URI contents on error pages.

Function: uri:path->keys path-list ptypes

path-list is a path-list as returned by uri:split-fields. uri:path->keys returns a list of items returned by uri:decode-path, coerced to types ptypes.

File-system Locators and Predicates

Function: path->uri path

Returns a URI-string for path on the local host.