501 lines
18 KiB
Scheme
501 lines
18 KiB
Scheme
;;;; optargs.scm -- support for optional arguments
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;;;;
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;;;; Copyright (C) 1997, 1998, 1999, 2001, 2002, 2004, 2006 Free Software Foundation, Inc.
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;;;;
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;;;; This library is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU Lesser General Public
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;;;; License as published by the Free Software Foundation; either
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;;;; version 3 of the License, or (at your option) any later version.
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;;;;
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;;;; This library is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;;; Lesser General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU Lesser General Public
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;;;; License along with this library; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;;;
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;;;; Contributed by Maciej Stachowiak <mstachow@alum.mit.edu>
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;;; Commentary:
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;;; {Optional Arguments}
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;;;
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;;; The C interface for creating Guile procedures has a very handy
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;;; "optional argument" feature. This module attempts to provide
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;;; similar functionality for procedures defined in Scheme with
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;;; a convenient and attractive syntax.
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;;;
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;;; exported macros are:
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;;; let-optional
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;;; let-optional*
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;;; let-keywords
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;;; let-keywords*
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;;; lambda*
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;;; define*
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;;; define*-public
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;;; defmacro*
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;;; defmacro*-public
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;;;
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;;;
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;;; Summary of the lambda* extended parameter list syntax (brackets
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;;; are used to indicate grouping only):
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;;;
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;;; ext-param-list ::= [identifier]* [#:optional [ext-var-decl]+]?
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;;; [#:key [ext-var-decl]+ [#:allow-other-keys]?]?
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;;; [[#:rest identifier]|[. identifier]]?
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;;;
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;;; ext-var-decl ::= identifier | ( identifier expression )
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;;;
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;;; The characters `*', `+' and `?' are not to be taken literally; they
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;;; mean respectively, zero or more occurences, one or more occurences,
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;;; and one or zero occurences.
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;;;
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;;; Code:
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;; (define-module (ice-9 optargs)
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;; #:use-module (system base pmatch)
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;; #:replace (lambda*)
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;; #:export-syntax (let-optional
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;; let-optional*
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;; let-keywords
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;; let-keywords*
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;; define*
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;; define*-public
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;; defmacro*
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;; defmacro*-public))
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;; let-optional rest-arg (binding ...) . body
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;; let-optional* rest-arg (binding ...) . body
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;; macros used to bind optional arguments
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;;
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;; These two macros give you an optional argument interface that is
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;; very "Schemey" and introduces no fancy syntax. They are compatible
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;; with the scsh macros of the same name, but are slightly
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;; extended. Each of binding may be of one of the forms <var> or
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;; (<var> <default-value>). rest-arg should be the rest-argument of
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;; the procedures these are used from. The items in rest-arg are
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;; sequentially bound to the variable namess are given. When rest-arg
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;; runs out, the remaining vars are bound either to the default values
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;; or to `#f' if no default value was specified. rest-arg remains
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;; bound to whatever may have been left of rest-arg.
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;;
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(defmacro let-optional (REST-ARG BINDINGS . BODY)
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(let-optional-template REST-ARG BINDINGS BODY 'let))
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(defmacro let-optional* (REST-ARG BINDINGS . BODY)
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(let-optional-template REST-ARG BINDINGS BODY 'let*))
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;; let-keywords rest-arg allow-other-keys? (binding ...) . body
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;; let-keywords* rest-arg allow-other-keys? (binding ...) . body
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;; macros used to bind keyword arguments
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;;
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;; These macros pick out keyword arguments from rest-arg, but do not
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;; modify it. This is consistent at least with Common Lisp, which
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;; duplicates keyword args in the rest arg. More explanation of what
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;; keyword arguments in a lambda list look like can be found below in
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;; the documentation for lambda*. Bindings can have the same form as
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;; for let-optional. If allow-other-keys? is false, an error will be
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;; thrown if anything that looks like a keyword argument but does not
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;; match a known keyword parameter will result in an error.
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;;
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(defmacro let-keywords (REST-ARG ALLOW-OTHER-KEYS? BINDINGS . BODY)
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(let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY 'let))
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(defmacro let-keywords* (REST-ARG ALLOW-OTHER-KEYS? BINDINGS . BODY)
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(let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY 'let*))
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;; some utility procedures for implementing the various let-forms.
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(define (let-o-k-template REST-ARG BINDINGS BODY let-type proc)
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(let ((bindings (map (lambda (x)
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(if (list? x)
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x
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(list x #f)))
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BINDINGS)))
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`(,let-type ,(map proc bindings) ,@BODY)))
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(define (let-optional-template REST-ARG BINDINGS BODY let-type)
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(if (null? BINDINGS)
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`(let () ,@BODY)
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(let-o-k-template REST-ARG BINDINGS BODY let-type
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(lambda (optional)
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`(,(car optional)
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(cond
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((not (null? ,REST-ARG))
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(let ((result (car ,REST-ARG)))
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,(list 'set! REST-ARG
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`(cdr ,REST-ARG))
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result))
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(else
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,(cadr optional))))))))
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(define (let-keywords-template REST-ARG ALLOW-OTHER-KEYS? BINDINGS BODY let-type)
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(if (null? BINDINGS)
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`(let () ,@BODY)
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(let* ((kb-list-gensym (gensym "kb:G"))
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(bindfilter (lambda (key)
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`(,(car key)
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(cond
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((assq ',(car key) ,kb-list-gensym)
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=> cdr)
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(else
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,(cadr key)))))))
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`(let ((,kb-list-gensym (;;(@@ (ice-9 optargs) rest-arg->keyword-binding-list)
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rest-arg->keyword-binding-list
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,REST-ARG ',(map (lambda (x) (symbol->keyword (if (pair? x) (car x) x)))
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BINDINGS)
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,ALLOW-OTHER-KEYS?)))
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,(let-o-k-template REST-ARG BINDINGS BODY let-type bindfilter)))))
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(define (rest-arg->keyword-binding-list rest-arg keywords allow-other-keys?)
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(if (null? rest-arg)
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'()
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(let loop ((first (car rest-arg))
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(rest (cdr rest-arg))
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(accum '()))
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(let ((next (lambda (a)
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(if (null? (cdr rest))
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a
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(loop (cadr rest) (cddr rest) a)))))
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(if (keyword? first)
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(cond
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((memq first keywords)
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(if (null? rest)
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(error "Keyword argument has no value.")
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(next (cons (cons (keyword->symbol first)
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(car rest)) accum))))
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((not allow-other-keys?)
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(error "Unknown keyword in arguments."))
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(else (if (null? rest)
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accum
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(next accum))))
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(if (null? rest)
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accum
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(loop (car rest) (cdr rest) accum)))))))
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;; lambda* args . body
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;; lambda extended for optional and keyword arguments
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;;
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;; lambda* creates a procedure that takes optional arguments. These
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;; are specified by putting them inside brackets at the end of the
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;; paramater list, but before any dotted rest argument. For example,
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;; (lambda* (a b #:optional c d . e) '())
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;; creates a procedure with fixed arguments a and b, optional arguments c
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;; and d, and rest argument e. If the optional arguments are omitted
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;; in a call, the variables for them are bound to `#f'.
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;;
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;; lambda* can also take keyword arguments. For example, a procedure
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;; defined like this:
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;; (lambda* (#:key xyzzy larch) '())
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;; can be called with any of the argument lists (#:xyzzy 11)
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;; (#:larch 13) (#:larch 42 #:xyzzy 19) (). Whichever arguments
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;; are given as keywords are bound to values.
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;;
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;; Optional and keyword arguments can also be given default values
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;; which they take on when they are not present in a call, by giving a
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;; two-item list in place of an optional argument, for example in:
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;; (lambda* (foo #:optional (bar 42) #:key (baz 73)) (list foo bar baz))
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;; foo is a fixed argument, bar is an optional argument with default
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;; value 42, and baz is a keyword argument with default value 73.
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;; Default value expressions are not evaluated unless they are needed
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;; and until the procedure is called.
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;;
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;; lambda* now supports two more special parameter list keywords.
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;;
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;; lambda*-defined procedures now throw an error by default if a
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;; keyword other than one of those specified is found in the actual
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;; passed arguments. However, specifying #:allow-other-keys
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;; immediately after the keyword argument declarations restores the
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;; previous behavior of ignoring unknown keywords. lambda* also now
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;; guarantees that if the same keyword is passed more than once, the
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;; last one passed is the one that takes effect. For example,
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;; ((lambda* (#:key (heads 0) (tails 0)) (display (list heads tails)))
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;; #:heads 37 #:tails 42 #:heads 99)
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;; would result in (99 47) being displayed.
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;;
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;; #:rest is also now provided as a synonym for the dotted syntax rest
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;; argument. The argument lists (a . b) and (a #:rest b) are equivalent in
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;; all respects to lambda*. This is provided for more similarity to DSSSL,
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;; MIT-Scheme and Kawa among others, as well as for refugees from other
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;; Lisp dialects.
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(defmacro lambda* (ARGLIST . BODY)
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(parse-arglist
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ARGLIST
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(lambda (non-optional-args optionals keys aok? rest-arg)
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;; Check for syntax errors.
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(if (not (every? symbol? non-optional-args))
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(error "Syntax error in fixed argument declaration."))
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(if (not (every? ext-decl? optionals))
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(error "Syntax error in optional argument declaration."))
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(if (not (every? ext-decl? keys))
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(error "Syntax error in keyword argument declaration."))
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(if (not (or (symbol? rest-arg) (eq? #f rest-arg)))
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(error "Syntax error in rest argument declaration."))
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;; generate the code.
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(let ((rest-gensym (or rest-arg (gensym "lambda*:G")))
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(lambda-gensym (gensym "lambda*:L")))
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(if (not (and (null? optionals) (null? keys)))
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`(let ((,lambda-gensym
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(lambda (,@non-optional-args . ,rest-gensym)
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;; Make sure that if the proc had a docstring, we put it
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;; here where it will be visible.
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,@(if (and (not (null? BODY))
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(string? (car BODY)))
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(list (car BODY))
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'())
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(let-optional*
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,rest-gensym
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,optionals
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(let-keywords* ,rest-gensym
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,aok?
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,keys
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,@(if (and (not rest-arg) (null? keys))
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`((if (not (null? ,rest-gensym))
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(error "Too many arguments.")))
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'())
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(let ()
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,@BODY))))))
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(set-procedure-property! ,lambda-gensym 'arglist
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'(,non-optional-args
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,optionals
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,keys
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,aok?
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,rest-arg))
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,lambda-gensym)
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`(lambda (,@non-optional-args . ,(if rest-arg rest-arg '()))
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,@BODY))))))
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(define (every? pred lst)
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(or (null? lst)
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(and (pred (car lst))
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(every? pred (cdr lst)))))
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(define (ext-decl? obj)
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(or (symbol? obj)
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(and (list? obj) (= 2 (length obj)) (symbol? (car obj)))))
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;; XXX - not tail recursive
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(define (improper-list-copy obj)
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(if (pair? obj)
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(cons (car obj) (improper-list-copy (cdr obj)))
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obj))
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(define (parse-arglist arglist cont)
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(define (split-list-at val lst cont)
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(cond
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((memq val lst)
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=> (lambda (pos)
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(if (memq val (cdr pos))
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(error (with-output-to-string
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(lambda ()
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(map display `(,val
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" specified more than once in argument list.")))))
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(cont (reverse (cdr (memq val (reverse lst)))) (cdr pos) #t))))
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(else (cont lst '() #f))))
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(define (parse-opt-and-fixed arglist keys aok? rest cont)
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(split-list-at
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#:optional arglist
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(lambda (before after split?)
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(if (and split? (null? after))
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(error "#:optional specified but no optional arguments declared.")
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(cont before after keys aok? rest)))))
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(define (parse-keys arglist rest cont)
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(split-list-at
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#:allow-other-keys arglist
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(lambda (aok-before aok-after aok-split?)
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(if (and aok-split? (not (null? aok-after)))
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(error "#:allow-other-keys not at end of keyword argument declarations.")
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(split-list-at
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#:key aok-before
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(lambda (key-before key-after key-split?)
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(cond
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((and aok-split? (not key-split?))
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(error "#:allow-other-keys specified but no keyword arguments declared."))
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(key-split?
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(cond
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((null? key-after) (error "#:key specified but no keyword arguments declared."))
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((memq #:optional key-after) (error "#:optional arguments declared after #:key arguments."))
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(else (parse-opt-and-fixed key-before key-after aok-split? rest cont))))
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(else (parse-opt-and-fixed arglist '() #f rest cont)))))))))
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(define (parse-rest arglist cont)
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(cond
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((null? arglist) (cont '() '() '() #f #f))
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((not (pair? arglist)) (cont '() '() '() #f arglist))
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((not (list? arglist))
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(let* ((copy (improper-list-copy arglist))
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(lp (last-pair copy))
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(ra (cdr lp)))
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(set-cdr! lp '())
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(if (memq #:rest copy)
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(error "Cannot specify both #:rest and dotted rest argument.")
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(parse-keys copy ra cont))))
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(else (split-list-at
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#:rest arglist
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(lambda (before after split?)
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(if split?
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(case (length after)
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((0) (error "#:rest not followed by argument."))
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((1) (parse-keys before (car after) cont))
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(else (error "#:rest argument must be declared last.")))
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(parse-keys before #f cont)))))))
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(parse-rest arglist cont))
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;; define* args . body
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;; define*-public args . body
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;; define and define-public extended for optional and keyword arguments
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;;
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;; define* and define*-public support optional arguments with
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;; a similar syntax to lambda*. They also support arbitrary-depth
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;; currying, just like Guile's define. Some examples:
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;; (define* (x y #:optional a (z 3) #:key w . u) (display (list y z u)))
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;; defines a procedure x with a fixed argument y, an optional agument
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;; a, another optional argument z with default value 3, a keyword argument w,
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;; and a rest argument u.
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;; (define-public* ((foo #:optional bar) #:optional baz) '())
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;; This illustrates currying. A procedure foo is defined, which,
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;; when called with an optional argument bar, returns a procedure that
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;; takes an optional argument baz.
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;;
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;; Of course, define*[-public] also supports #:rest and #:allow-other-keys
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;; in the same way as lambda*.
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(defmacro define* (ARGLIST . BODY)
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(define*-guts 'define ARGLIST BODY))
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(defmacro define*-public (ARGLIST . BODY)
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(define*-guts 'define-public ARGLIST BODY))
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;; The guts of define* and define*-public.
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(define (define*-guts DT ARGLIST BODY)
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(define (nest-lambda*s arglists)
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(if (null? arglists)
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BODY
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`((lambda* ,(car arglists) ,@(nest-lambda*s (cdr arglists))))))
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(define (define*-guts-helper ARGLIST arglists)
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(let ((first (car ARGLIST))
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(al (cons (cdr ARGLIST) arglists)))
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(if (symbol? first)
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`(,DT ,first ,@(nest-lambda*s al))
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(define*-guts-helper first al))))
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(if (symbol? ARGLIST)
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`(,DT ,ARGLIST ,@BODY)
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(define*-guts-helper ARGLIST '())))
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;; defmacro* name args . body
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;; defmacro*-public args . body
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;; defmacro and defmacro-public extended for optional and keyword arguments
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;;
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;; These are just like defmacro and defmacro-public except that they
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;; take lambda*-style extended paramter lists, where #:optional,
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;; #:key, #:allow-other-keys and #:rest are allowed with the usual
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;; semantics. Here is an example of a macro with an optional argument:
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;; (defmacro* transmorgify (a #:optional b)
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(defmacro defmacro* (NAME ARGLIST . BODY)
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`(define-macro ,NAME #f (lambda* ,ARGLIST ,@BODY)))
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(defmacro defmacro*-public (NAME ARGLIST . BODY)
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`(begin
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(defmacro* ,NAME ,ARGLIST ,@BODY)
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(export-syntax ,NAME)))
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;;; Support for optional & keyword args with the interpreter.
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(define *uninitialized* (list 'uninitialized))
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(define (parse-lambda-case spec inits predicate args)
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(pmatch spec
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((,nreq ,nopt ,rest-idx ,nargs ,allow-other-keys? ,kw-indices)
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(define (req args prev tail n)
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(cond
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((zero? n)
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(if prev (set-cdr! prev '()))
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(let ((slots-tail (make-list (- nargs nreq) *uninitialized*)))
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(opt (if prev (append! args slots-tail) slots-tail)
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slots-tail tail nopt inits)))
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((null? tail)
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#f) ;; fail
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(else
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(req args tail (cdr tail) (1- n)))))
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(define (opt slots slots-tail args-tail n inits)
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(cond
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((zero? n)
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(rest-or-key slots slots-tail args-tail inits rest-idx))
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((null? args-tail)
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(set-car! slots-tail (apply (car inits) slots))
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(opt slots (cdr slots-tail) '() (1- n) (cdr inits)))
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(else
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(set-car! slots-tail (car args-tail))
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(opt slots (cdr slots-tail) (cdr args-tail) (1- n) (cdr inits)))))
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(define (rest-or-key slots slots-tail args-tail inits rest-idx)
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(cond
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(rest-idx
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;; it has to be this way, vars are allocated in this order
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(set-car! slots-tail args-tail)
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(if (pair? kw-indices)
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(key slots (cdr slots-tail) args-tail inits)
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(rest-or-key slots (cdr slots-tail) '() inits #f)))
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((pair? kw-indices)
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;; fail early here, because once we're in keyword land we throw
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;; errors instead of failing
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(and (or (null? args-tail) rest-idx (keyword? (car args-tail)))
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(key slots slots-tail args-tail inits)))
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((pair? args-tail)
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#f) ;; fail
|
||
(else
|
||
(pred slots))))
|
||
(define (key slots slots-tail args-tail inits)
|
||
(cond
|
||
((null? args-tail)
|
||
(if (null? inits)
|
||
(pred 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)
|
||
(error "bad keyword argument list" 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 (error "unrecognized keyword" args-tail))))
|
||
(define (pred slots)
|
||
(cond
|
||
(predicate
|
||
(if (apply predicate slots)
|
||
slots
|
||
#f))
|
||
(else slots)))
|
||
(let ((args (list-copy args)))
|
||
(req args #f args nreq)))
|
||
(else (error "unexpected spec" spec))))
|