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;;;; optargs.scm -- support for optional arguments
;;;;
;;;; Copyright (C) 1997, 1998, 1999, 2001, 2002, 2004, 2006, 2009, 2010, 2011 Free Software Foundation, Inc.
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;;;
;;;; Contributed by Maciej Stachowiak <[email protected]>
;;; Commentary:
;;; {Optional Arguments}
;;;
;;; The C interface for creating Guile procedures has a very handy
;;; "optional argument" feature. This module attempts to provide
;;; similar functionality for procedures defined in Scheme with
;;; a convenient and attractive syntax.
;;;
;;; exported macros are:
;;; let-optional
;;; let-optional*
;;; let-keywords
;;; let-keywords*
;;; lambda*
;;; define*
;;; define*-public
;;; defmacro*
;;; defmacro*-public
;;;
;;;
;;; Summary of the lambda* extended parameter list syntax (brackets
;;; are used to indicate grouping only):
;;;
;;; ext-param-list ::= [identifier]* [#:optional [ext-var-decl]+]?
;;; [#:key [ext-var-decl]+ [#:allow-other-keys]?]?
;;; [[#:rest identifier]|[. identifier]]?
;;;
;;; ext-var-decl ::= identifier | ( identifier expression )
;;;
;;; The characters `*', `+' and `?' are not to be taken literally; they
;;; mean respectively, zero or more occurences, one or more occurences,
;;; and one or zero occurences.
;;;
;;; Code:
(define-module (ice-9 optargs)
#:use-module (system base pmatch)
#:re-export (lambda* define*)
#:export (let-optional
let-optional*
let-keywords
let-keywords*
define*-public
defmacro*
defmacro*-public))
;; let-optional rest-arg (binding ...) . body
;; let-optional* rest-arg (binding ...) . body
;; macros used to bind optional arguments
;;
;; These two macros give you an optional argument interface that is
;; very "Schemey" and introduces no fancy syntax. They are compatible
;; with the scsh macros of the same name, but are slightly
;; extended. Each of binding may be of one of the forms <var> or
;; (<var> <default-value>). rest-arg should be the rest-argument of
;; the procedures these are used from. The items in rest-arg are
;; sequentially bound to the variable namess are given. When rest-arg
;; runs out, the remaining vars are bound either to the default values
;; or to `#f' if no default value was specified. rest-arg remains
;; bound to whatever may have been left of rest-arg.
;;
(define (vars&inits bindings)
(let lp ((bindings bindings) (vars '()) (inits '()))
(syntax-case bindings ()
(()
(values (reverse vars) (reverse inits)))
(((v init) . rest) (identifier? #'v)
(lp #'rest (cons #'v vars) (cons #'init inits)))
((v . rest) (identifier? #'v)
(lp #'rest (cons #'v vars) (cons #'#f inits))))))
(define-syntax let-optional
(lambda (x)
(syntax-case x ()
((_ rest-arg (binding ...) b0 b1 ...) (identifier? #'rest-arg)
(call-with-values (lambda () (vars&inits #'(binding ...)))
(lambda (vars inits)
(with-syntax ((n (length vars))
(n+1 (1+ (length vars)))
(vars (append vars (list #'rest-arg)))
((t ...) (generate-temporaries vars))
((i ...) inits))
#'(let ((t (lambda vars i))
...)
(apply (lambda vars b0 b1 ...)
(or (parse-lambda-case '(0 n n n+1 #f '())
(list t ...)
rest-arg)
(error "sth" rest-arg)))))))))))
(define-syntax let-optional*
(lambda (x)
(syntax-case x ()
((_ rest-arg (binding ...) b0 b1 ...) (identifier? #'rest-arg)
(call-with-values (lambda () (vars&inits #'(binding ...)))
(lambda (vars inits)
(with-syntax ((n (length vars))
(n+1 (1+ (length vars)))
(vars (append vars (list #'rest-arg)))
((i ...) inits))
#'(apply (lambda vars b0 b1 ...)
(or (parse-lambda-case '(0 n n n+1 #f '())
(list (lambda vars i) ...)
rest-arg)
(error "sth" rest-arg))))))))))
;; let-keywords rest-arg allow-other-keys? (binding ...) . body
;; let-keywords* rest-arg allow-other-keys? (binding ...) . body
;; macros used to bind keyword arguments
;;
;; These macros pick out keyword arguments from rest-arg, but do not
;; modify it. This is consistent at least with Common Lisp, which
;; duplicates keyword args in the rest arg. More explanation of what
;; keyword arguments in a lambda list look like can be found below in
;; the documentation for lambda*. Bindings can have the same form as
;; for let-optional. If allow-other-keys? is false, an error will be
;; thrown if anything that looks like a keyword argument but does not
;; match a known keyword parameter will result in an error.
;;
(define-syntax let-keywords
(lambda (x)
(syntax-case x ()
((_ rest-arg aok (binding ...) b0 b1 ...) (identifier? #'rest-arg)
(call-with-values (lambda () (vars&inits #'(binding ...)))
(lambda (vars inits)
(with-syntax ((n (length vars))
(vars vars)
(ivars (generate-temporaries vars))
((kw ...) (map symbol->keyword
(map syntax->datum vars)))
((idx ...) (iota (length vars)))
((t ...) (generate-temporaries vars))
((i ...) inits))
#'(let ((t (lambda ivars i))
...)
(apply (lambda vars b0 b1 ...)
(or (parse-lambda-case '(0 0 #f n aok ((kw . idx) ...))
(list t ...)
rest-arg)
(error "sth" rest-arg))))))))
((_ rest-arg aok (binding ...) b0 b1 ...)
#'(let ((r rest-arg))
(let-keywords r aok (binding ...) b0 b1 ...))))))
(define-syntax let-keywords*
(lambda (x)
(syntax-case x ()
((_ rest-arg aok (binding ...) b0 b1 ...) (identifier? #'rest-arg)
(call-with-values (lambda () (vars&inits #'(binding ...)))
(lambda (vars inits)
(with-syntax ((n (length vars))
(vars vars)
((kw ...) (map symbol->keyword
(map syntax->datum vars)))
((idx ...) (iota (length vars)))
((i ...) inits))
#'(apply (lambda vars b0 b1 ...)
(or (parse-lambda-case '(0 0 #f n aok ((kw . idx) ...))
(list (lambda vars i) ...)
rest-arg)
(error "sth" rest-arg)))))))
((_ rest-arg aok (binding ...) b0 b1 ...)
#'(let ((r rest-arg))
(let-keywords* r aok (binding ...) b0 b1 ...))))))
;; lambda* args . body
;; lambda extended for optional and keyword arguments
;;
;; lambda* creates a procedure that takes optional arguments. These
;; are specified by putting them inside brackets at the end of the
;; parameter list, but before any dotted rest argument. For example,
;; (lambda* (a b #:optional c d . e) '())
;; creates a procedure with fixed arguments a and b, optional arguments c
;; and d, and rest argument e. If the optional arguments are omitted
;; in a call, the variables for them are bound to `#f'.
;;
;; lambda* can also take keyword arguments. For example, a procedure
;; defined like this:
;; (lambda* (#:key xyzzy larch) '())
;; can be called with any of the argument lists (#:xyzzy 11)
;; (#:larch 13) (#:larch 42 #:xyzzy 19) (). Whichever arguments
;; are given as keywords are bound to values.
;;
;; Optional and keyword arguments can also be given default values
;; which they take on when they are not present in a call, by giving a
;; two-item list in place of an optional argument, for example in:
;; (lambda* (foo #:optional (bar 42) #:key (baz 73)) (list foo bar baz))
;; foo is a fixed argument, bar is an optional argument with default
;; value 42, and baz is a keyword argument with default value 73.
;; Default value expressions are not evaluated unless they are needed
;; and until the procedure is called.
;;
;; lambda* now supports two more special parameter list keywords.
;;
;; lambda*-defined procedures now throw an error by default if a
;; keyword other than one of those specified is found in the actual
;; passed arguments. However, specifying #:allow-other-keys
;; immediately after the keyword argument declarations restores the
;; previous behavior of ignoring unknown keywords. lambda* also now
;; guarantees that if the same keyword is passed more than once, the
;; last one passed is the one that takes effect. For example,
;; ((lambda* (#:key (heads 0) (tails 0)) (display (list heads tails)))
;; #:heads 37 #:tails 42 #:heads 99)
;; would result in (99 47) being displayed.
;;
;; #:rest is also now provided as a synonym for the dotted syntax rest
;; argument. The argument lists (a . b) and (a #:rest b) are equivalent in
;; all respects to lambda*. This is provided for more similarity to DSSSL,
;; MIT-Scheme and Kawa among others, as well as for refugees from other
;; Lisp dialects.
;; define* args . body
;; define*-public args . body
;; define and define-public extended for optional and keyword arguments
;;
;; define* and define*-public support optional arguments with
;; a similar syntax to lambda*. Some examples:
;; (define* (x y #:optional a (z 3) #:key w . u) (display (list y z u)))
;; defines a procedure x with a fixed argument y, an optional agument
;; a, another optional argument z with default value 3, a keyword argument w,
;; and a rest argument u.
;;
;; Of course, define*[-public] also supports #:rest and #:allow-other-keys
;; in the same way as lambda*.
(define-syntax define*-public
(lambda (x)
(syntax-case x ()
((_ (id . args) b0 b1 ...)
#'(define-public id (lambda* args b0 b1 ...)))
((_ id val) (identifier? #'id)
#'(define-public id val)))))
;; defmacro* name args . body
;; defmacro*-public args . body
;; defmacro and defmacro-public extended for optional and keyword arguments
;;
;; These are just like defmacro and defmacro-public except that they
;; take lambda*-style extended paramter lists, where #:optional,
;; #:key, #:allow-other-keys and #:rest are allowed with the usual
;; semantics. Here is an example of a macro with an optional argument:
;; (defmacro* transmogrify (a #:optional b)
(define-syntax defmacro*
(lambda (x)
(syntax-case x ()
((_ id args doc b0 b1 ...) (string? (syntax->datum #'doc))
#'(define-macro id doc (lambda* args b0 b1 ...)))
((_ id args b0 b1 ...)
#'(define-macro id #f (lambda* args b0 b1 ...))))))
(define-syntax-rule (defmacro*-public id args b0 b1 ...)
(begin
(defmacro* id args b0 b1 ...)
(export-syntax id)))
;;; Support for optional & keyword args with the interpreter.
(define *uninitialized* (list 'uninitialized))
(define (parse-lambda-case spec inits args)
(pmatch spec
((,nreq ,nopt ,rest-idx ,nargs ,allow-other-keys? ,kw-indices)
(define (req args prev tail n)
(cond
((zero? n)
(if prev (set-cdr! prev '()))
(let ((slots-tail (make-list (- nargs nreq) *uninitialized*)))
(opt (if prev (append! args slots-tail) slots-tail)
slots-tail tail nopt inits)))
((null? tail)
#f) ;; fail
(else
(req args tail (cdr tail) (1- n)))))
(define (opt slots slots-tail args-tail n inits)
(cond
((zero? n)
(rest-or-key slots slots-tail args-tail inits rest-idx))
((null? args-tail)
(set-car! slots-tail (apply (car inits) slots))
(opt slots (cdr slots-tail) '() (1- n) (cdr inits)))
(else
(set-car! slots-tail (car args-tail))
(opt slots (cdr slots-tail) (cdr args-tail) (1- n) (cdr inits)))))
(define (rest-or-key slots slots-tail args-tail inits rest-idx)
(cond
(rest-idx
;; it has to be this way, vars are allocated in this order
(set-car! slots-tail args-tail)
(if (pair? kw-indices)
(permissive-keys slots (cdr slots-tail) args-tail inits)
(rest-or-key slots (cdr slots-tail) '() inits #f)))
((pair? kw-indices)
;; fail early here, because once we're in keyword land we throw
;; errors instead of failing
(and (or (null? args-tail) rest-idx (keyword? (car args-tail)))
(key slots slots-tail args-tail inits)))
((pair? args-tail)
#f) ;; fail
(else
slots)))
(define (permissive-keys slots slots-tail args-tail inits)
(cond
((null? args-tail)
(if (null? inits)
slots
(begin
(if (eq? (car slots-tail) *uninitialized*)
(set-car! slots-tail (apply (car inits) slots)))
(permissive-keys slots (cdr slots-tail) '() (cdr inits)))))
((not (keyword? (car args-tail)))
(permissive-keys slots slots-tail (cdr args-tail) inits))
((and (keyword? (car args-tail))
(pair? (cdr args-tail))
(assq-ref kw-indices (car args-tail)))
=> (lambda (i)
(list-set! slots i (cadr args-tail))
(permissive-keys slots slots-tail (cddr args-tail) inits)))
((and (keyword? (car args-tail))
(pair? (cdr args-tail))
allow-other-keys?)
(permissive-keys slots slots-tail (cddr args-tail) inits))
(else (scm-error 'keyword-argument-error #f "Unrecognized keyword"
'() args-tail))))
(define (key slots slots-tail args-tail inits)
(cond
((null? args-tail)
(if (null? inits)
slots
(begin
(if (eq? (car slots-tail) *uninitialized*)
(set-car! slots-tail (apply (car inits) slots)))
(key slots (cdr slots-tail) '() (cdr inits)))))
((not (keyword? (car args-tail)))
(if rest-idx
;; no error checking, everything goes to the rest..
(key slots slots-tail '() inits)
(scm-error 'keyword-argument-error #f "Invalid keyword"
'() args-tail)))
((and (keyword? (car args-tail))
(pair? (cdr args-tail))
(assq-ref kw-indices (car args-tail)))
=> (lambda (i)
(list-set! slots i (cadr args-tail))
(key slots slots-tail (cddr args-tail) inits)))
((and (keyword? (car args-tail))
(pair? (cdr args-tail))
allow-other-keys?)
(key slots slots-tail (cddr args-tail) inits))
(else (scm-error 'keyword-argument-error #f "Unrecognized keyword"
'() args-tail))))
(let ((args (list-copy args)))
(req args #f args nreq)))
(else (error "unexpected spec" spec))))
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