251 lines
10 KiB
Scheme
251 lines
10 KiB
Scheme
;; -*-scheme-*-
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(define (syntax-error message thing)
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(display "syntax-error:")
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(display message)
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(display ":")
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;;(display thing)
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(newline))
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;;; Adapted from scheme48-1.1/scheme/alt/syntax.scm
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;;; Copyright (c) 1993-2004 by Richard Kelsey and Jonathan Rees. See file COPYING.
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;;; scheme48-1.1/COPYING
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;; Copyright (c) 1993-2004 Richard Kelsey and Jonathan Rees
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;; All rights reserved.
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;; Redistribution and use in source and binary forms, with or without
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;; modification, are permitted provided that the following conditions
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;; are met:
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;; 1. Redistributions of source code must retain the above copyright
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;; notice, this list of conditions and the following disclaimer.
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;; 2. Redistributions in binary form must reproduce the above copyright
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;; notice, this list of conditions and the following disclaimer in the
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;; documentation and/or other materials provided with the distribution.
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;; 3. The name of the authors may not be used to endorse or promote products
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;; derived from this software without specific prior written permission.
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;; THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
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;; IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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;; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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;; IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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;; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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;; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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;; DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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;; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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;; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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;; THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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(display "mes:define-syntax...")
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(define-macro (define-syntax macro-name transformer . stuff)
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`(define-macro (,macro-name . args)
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(,transformer (cons ',macro-name args)
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(lambda (x) x)
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eq?)))
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;; Rewrite-rule compiler (a.k.a. "extend-syntax")
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;; Example:
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;;
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;; (define-syntax or
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;; (syntax-rules ()
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;; ((or) #f)
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;; ((or e) e)
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;; ((or e1 e ...) (let ((temp e1))
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;; (if temp temp (or e ...))))))
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(newline)
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(display "mes:define-syntax syntax-rules...")
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(newline)
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(define-syntax syntax-rules
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(let ()
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(define name? symbol?)
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(define (segment-pattern? pattern)
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(and (segment-template? pattern)
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(or (null? (cddr pattern))
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(syntax-error "segment matching not implemented" pattern))))
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(define (segment-template? pattern)
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(and (pair? pattern)
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(pair? (cdr pattern))
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(memq (cadr pattern) indicators-for-zero-or-more)))
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(define indicators-for-zero-or-more (list (string->symbol "...") '---))
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(lambda (exp r c)
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(define %input (r '%input)) ;Gensym these, if you like.
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(define %compare (r '%compare))
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(define %rename (r '%rename))
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(define %tail (r '%tail))
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(define %temp (r '%temp))
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(define rules (cddr exp))
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(define subkeywords (cadr exp))
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(define (make-transformer rules)
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`(lambda (,%input ,%rename ,%compare)
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(let ((,%tail (cdr ,%input)))
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(cond ,@(map process-rule rules)
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(else
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(syntax-error
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"use of macro doesn't match definition"
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,%input))))))
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(define (process-rule rule)
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(cond ((and (pair? rule)
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(pair? (cdr rule))
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(null? (cddr rule)))
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(let ((pattern (cdar rule))
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(template (cadr rule)))
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`((and ,@(process-match %tail pattern))
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(let* ,(process-pattern pattern
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%tail
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(lambda (x) x))
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,(process-template template
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0
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(meta-variables pattern 0 '()))))))
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(syntax-error "ill-formed syntax rule" rule)))
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;; Generate code to test whether input expression matches pattern
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(define (process-match input pattern)
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(cond ((name? pattern)
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(cond ((member pattern subkeywords)
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`((,%compare ,input (,%rename ',pattern))))
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(#t `())))
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((segment-pattern? pattern)
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(process-segment-match input (car pattern)))
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((pair? pattern)
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`((let ((,%temp ,input))
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(and (pair? ,%temp)
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,@(process-match `(car ,%temp) (car pattern))
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,@(process-match `(cdr ,%temp) (cdr pattern))))))
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((or (null? pattern) (boolean? pattern) (char? pattern))
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`((eq? ,input ',pattern)))
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(else
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`((equal? ,input ',pattern)))))
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(define (process-segment-match input pattern)
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(let ((conjuncts (process-match '(car l) pattern)))
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(cond ((null? conjuncts)
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`((list? ,input))) ;+++
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(#t `((let loop ((l ,input))
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(or (null? l)
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(and (pair? l)
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,@conjuncts
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(loop (cdr l))))))))))
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;; Generate code to take apart the input expression
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;; This is pretty bad, but it seems to work (can't say why).
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(define (process-pattern pattern path mapit)
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(cond ((name? pattern)
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(cond ((memq pattern subkeywords)
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'())
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(#t
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(list (list pattern (mapit path))))))
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((segment-pattern? pattern)
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(process-pattern (car pattern)
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%temp
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(lambda (x) ;temp is free in x
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(mapit (cond ((eq? %temp x)
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path) ;+++
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(#t
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`(map (lambda (,%temp) ,x)
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,path)))))))
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((pair? pattern)
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(append (process-pattern (car pattern) `(car ,path) mapit)
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(process-pattern (cdr pattern) `(cdr ,path) mapit)))
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(else '())))
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;; Generate code to compose the output expression according to template
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(define (process-template template rank env)
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(cond ((name? template)
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(let ((probe (assq template env)))
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(cond (probe
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(cond ((<= (cdr probe) rank)
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template)
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(#t (syntax-error "template rank error (too few ...'s?)"
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template))))
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(#t `(,%rename ',template)))))
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((segment-template? template)
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(let ((vars
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(free-meta-variables (car template) (+ rank 1) env '())))
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(cond ((null? vars)
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(syntax-error "too many ...'s" template))
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(#t (let* ((x (process-template (car template)
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(+ rank 1)
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env))
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(gen (cond ((equal? (list x) vars)
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x) ;+++
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(#t `(map (lambda ,vars ,x)
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,@vars)))))
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(cond ((null? (cddr template))
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gen) ;+++
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(else
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`(append ,gen ,(process-template (cddr template)
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rank env)))))))))
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((pair? template)
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`(cons ,(process-template (car template) rank env)
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,(process-template (cdr template) rank env)))
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(else `(quote ,template))))
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;; Return an association list of (var . rank)
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(define (meta-variables pattern rank vars)
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(cond ((name? pattern)
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(cond ((memq pattern subkeywords)
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vars)
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(else (cons (cons pattern rank) vars))))
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((segment-pattern? pattern)
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(meta-variables (car pattern) (+ rank 1) vars))
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((pair? pattern)
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(meta-variables (car pattern) rank
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(meta-variables (cdr pattern) rank vars)))
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(else vars)))
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;; Return a list of meta-variables of given higher rank
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(define (free-meta-variables template rank env free)
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(cond ((name? template)
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(cond ((and (not (memq template free))
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(let ((probe (assq template env)))
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(and probe (>= (cdr probe) rank))))
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(cons template free))
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(else free)))
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((segment-template? template)
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(free-meta-variables (car template)
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rank env
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(free-meta-variables (cddr template)
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rank env free)))
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((pair? template)
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(free-meta-variables (car template)
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rank env
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(free-meta-variables (cdr template)
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rank env free)))
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(else free)))
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c ;ignored
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;; Kludge for Scheme48 linker.
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;; `(cons ,(make-transformer rules)
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;; ',(find-free-names-in-syntax-rules subkeywords rules))
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(make-transformer rules))))
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(define-macro (define-syntax-rule id-pattern . template)
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`(define-syntax ,(car id-pattern)
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(syntax-rules ()
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((,(car id-pattern) . ,(cdr id-pattern)) ,@template))))
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(define else #t)
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