;;; "synrul.scm" Rule-based Syntactic Expanders -*-Scheme-*-
;;; Copyright (c) 1989-91 Massachusetts Institute of Technology
;;;
;;; This material was developed by the Scheme project at the
;;; Massachusetts Institute of Technology, Department of Electrical
;;; Engineering and Computer Science. Permission to copy and modify
;;; this software, to redistribute either the original software or a
;;; modified version, and to use this software for any purpose is
;;; granted, subject to the following restrictions and understandings.
;;;
;;; 1. Any copy made of this software must include this copyright
;;; notice in full.
;;;
;;; 2. Users of this software agree to make their best efforts (a) to
;;; return to the MIT Scheme project any improvements or extensions
;;; that they make, so that these may be included in future releases;
;;; and (b) to inform MIT of noteworthy uses of this software.
;;;
;;; 3. All materials developed as a consequence of the use of this
;;; software shall duly acknowledge such use, in accordance with the
;;; usual standards of acknowledging credit in academic research.
;;;
;;; 4. MIT has made no warranty or representation that the operation
;;; of this software will be error-free, and MIT is under no
;;; obligation to provide any services, by way of maintenance, update,
;;; or otherwise.
;;;
;;; 5. In conjunction with products arising from the use of this
;;; material, there shall be no use of the name of the Massachusetts
;;; Institute of Technology nor of any adaptation thereof in any
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;;;; Rule-based Syntactic Expanders
;;; See "Syntactic Extensions in the Programming Language Lisp", by
;;; Eugene Kohlbecker, Ph.D. dissertation, Indiana University, 1986.
;;; See also "Macros That Work", by William Clinger and Jonathan Rees
;;; (reference? POPL?). This implementation is derived from an
;;; implementation by Kent Dybvig, and includes some ideas from
;;; another implementation by Jonathan Rees.
;;; The expansion of SYNTAX-RULES references the following keywords:
;;; ER-TRANSFORMER LAMBDA IF BEGIN SET! QUOTE
;;; and the following procedures:
;;; CAR CDR NULL? PAIR? EQUAL? MAP LIST CONS APPEND
;;; ILL-FORMED-SYNTAX
;;; it also uses the anonymous keyword SYNTAX-QUOTE.
;;; For testing.
;;;(define (run-sr form)
;;; (expand/syntax-rules form (lambda (x) x) eq?))
(define (make-syntax-rules-macrology)
(make-er-expander-macrology
(lambda (define-classifier base-environment)
base-environment ;ignore
(define-classifier 'SYNTAX-RULES expand/syntax-rules))))
(define (expand/syntax-rules form rename compare)
(if (syntax-match? '((* IDENTIFIER) + ((IDENTIFIER . DATUM) EXPRESSION))
(cdr form))
(let ((keywords (cadr form))
(clauses (cddr form)))
(if (let loop ((keywords keywords))
(and (pair? keywords)
(or (memq (car keywords) (cdr keywords))
(loop (cdr keywords)))))
(syntax-error "keywords list contains duplicates" keywords)
(let ((r-form (rename 'FORM))
(r-rename (rename 'RENAME))
(r-compare (rename 'COMPARE)))
`(,(rename 'ER-TRANSFORMER)
(,(rename 'LAMBDA)
(,r-form ,r-rename ,r-compare)
,(let loop ((clauses clauses))
(if (null? clauses)
`(,(rename 'ILL-FORMED-SYNTAX) ,r-form)
(let ((pattern (caar clauses)))
(let ((sids
(parse-pattern rename compare keywords
pattern r-form)))
`(,(rename 'IF)
,(generate-match rename compare keywords
r-rename r-compare
pattern r-form)
,(generate-output rename compare r-rename
sids (cadar clauses)
syntax-error)
,(loop (cdr clauses))))))))))))
(ill-formed-syntax form)))
(define (parse-pattern rename compare keywords pattern expression)
(let loop
((pattern pattern)
(expression expression)
(sids '())
(control #f))
(cond ((identifier? pattern)
(if (memq pattern keywords)
sids
(cons (make-sid pattern expression control) sids)))
((and (or (zero-or-more? pattern rename compare)
(at-least-one? pattern rename compare))
(null? (cddr pattern)))
(let ((variable ((make-name-generator) 'CONTROL)))
(loop (car pattern)
variable
sids
(make-sid variable expression control))))
((pair? pattern)
(loop (car pattern)
`(,(rename 'CAR) ,expression)
(loop (cdr pattern)
`(,(rename 'CDR) ,expression)
sids
control)
control))
(else sids))))
(define (generate-match rename compare keywords r-rename r-compare
pattern expression)
(letrec
((loop
(lambda (pattern expression)
(cond ((identifier? pattern)
(if (memq pattern keywords)
(let ((temp (rename 'TEMP)))
`((,(rename 'LAMBDA)
(,temp)
(,(rename 'IF)
(,(rename 'IDENTIFIER?) ,temp)
(,r-compare ,temp
(,r-rename ,(syntax-quote pattern)))
#f))
,expression))
`#t))
((and (zero-or-more? pattern rename compare)
(null? (cddr pattern)))
(do-list (car pattern) expression))
((and (at-least-one? pattern rename compare)
(null? (cddr pattern)))
`(,(rename 'IF) (,(rename 'NULL?) ,expression)
#F
,(do-list (car pattern) expression)))
((pair? pattern)
(let ((generate-pair
(lambda (expression)
(conjunction
`(,(rename 'PAIR?) ,expression)
(conjunction
(loop (car pattern)
`(,(rename 'CAR) ,expression))
(loop (cdr pattern)
`(,(rename 'CDR) ,expression)))))))
(if (identifier? expression)
(generate-pair expression)
(let ((temp (rename 'TEMP)))
`((,(rename 'LAMBDA) (,temp) ,(generate-pair temp))
,expression)))))
((null? pattern)
`(,(rename 'NULL?) ,expression))
(else
`(,(rename 'EQUAL?) ,expression
(,(rename 'QUOTE) ,pattern))))))
(do-list
(lambda (pattern expression)
(let ((r-loop (rename 'LOOP))
(r-l (rename 'L))
(r-lambda (rename 'LAMBDA)))
`(((,r-lambda
(,r-loop)
(,(rename 'BEGIN)
(,(rename 'SET!)
,r-loop
(,r-lambda
(,r-l)
(,(rename 'IF)
(,(rename 'NULL?) ,r-l)
#T
,(conjunction
`(,(rename 'PAIR?) ,r-l)
(conjunction (loop pattern `(,(rename 'CAR) ,r-l))
`(,r-loop (,(rename 'CDR) ,r-l)))))))
,r-loop))
#F)
,expression))))
(conjunction
(lambda (predicate consequent)
(cond ((eq? predicate #T) consequent)
((eq? consequent #T) predicate)
(else `(,(rename 'IF) ,predicate ,consequent #F))))))
(loop pattern expression)))
(define (generate-output rename compare r-rename sids template syntax-error)
(let loop ((template template) (ellipses '()))
(cond ((identifier? template)
(let ((sid
(let loop ((sids sids))
(and (not (null? sids))
(if (eq? (sid-name (car sids)) template)
(car sids)
(loop (cdr sids)))))))
(if sid
(begin
(add-control! sid ellipses syntax-error)
(sid-expression sid))
`(,r-rename ,(syntax-quote template)))))
((or (zero-or-more? template rename compare)
(at-least-one? template rename compare))
(optimized-append rename compare
(let ((ellipsis (make-ellipsis '())))
(generate-ellipsis rename
ellipsis
(loop (car template)
(cons ellipsis
ellipses))))
(loop (cddr template) ellipses)))
((pair? template)
(optimized-cons rename compare
(loop (car template) ellipses)
(loop (cdr template) ellipses)))
(else
`(,(rename 'QUOTE) ,template)))))
(define (add-control! sid ellipses syntax-error)
(let loop ((sid sid) (ellipses ellipses))
(let ((control (sid-control sid)))
(cond (control
(if (null? ellipses)
(syntax-error "missing ellipsis in expansion" #f)
(let ((sids (ellipsis-sids (car ellipses))))
(cond ((not (memq control sids))
(set-ellipsis-sids! (car ellipses)
(cons control sids)))
((not (eq? control (car sids)))
(syntax-error "illegal control/ellipsis combination"
control sids)))))
(loop control (cdr ellipses)))
((not (null? ellipses))
(syntax-error "extra ellipsis in expansion" #f))))))
(define (generate-ellipsis rename ellipsis body)
(let ((sids (ellipsis-sids ellipsis)))
(let ((name (sid-name (car sids)))
(expression (sid-expression (car sids))))
(cond ((and (null? (cdr sids))
(eq? body name))
expression)
((and (null? (cdr sids))
(pair? body)
(pair? (cdr body))
(eq? (cadr body) name)
(null? (cddr body)))
`(,(rename 'MAP) ,(car body) ,expression))
(else
`(,(rename 'MAP) (,(rename 'LAMBDA) ,(map sid-name sids) ,body)
,@(map sid-expression sids)))))))
(define (zero-or-more? pattern rename compare)
(and (pair? pattern)
(pair? (cdr pattern))
(identifier? (cadr pattern))
(compare (cadr pattern) (rename '...))))
(define (at-least-one? pattern rename compare)
;;; (and (pair? pattern)
;;; (pair? (cdr pattern))
;;; (identifier? (cadr pattern))
;;; (compare (cadr pattern) (rename '+)))
pattern rename compare ;ignore
#f)
(define (optimized-cons rename compare a d)
(cond ((and (pair? d)
(compare (car d) (rename 'QUOTE))
(pair? (cdr d))
(null? (cadr d))
(null? (cddr d)))
`(,(rename 'LIST) ,a))
((and (pair? d)
(compare (car d) (rename 'LIST))
(list? (cdr d)))
`(,(car d) ,a ,@(cdr d)))
(else
`(,(rename 'CONS) ,a ,d))))
(define (optimized-append rename compare x y)
(if (and (pair? y)
(compare (car y) (rename 'QUOTE))
(pair? (cdr y))
(null? (cadr y))
(null? (cddr y)))
x
`(,(rename 'APPEND) ,x ,y)))
(define sid-type
(make-record-type "sid" '(NAME EXPRESSION CONTROL OUTPUT-EXPRESSION)))
(define make-sid
(record-constructor sid-type '(NAME EXPRESSION CONTROL)))
(define sid-name
(record-accessor sid-type 'NAME))
(define sid-expression
(record-accessor sid-type 'EXPRESSION))
(define sid-control
(record-accessor sid-type 'CONTROL))
(define sid-output-expression
(record-accessor sid-type 'OUTPUT-EXPRESSION))
(define set-sid-output-expression!
(record-modifier sid-type 'OUTPUT-EXPRESSION))
(define ellipsis-type
(make-record-type "ellipsis" '(SIDS)))
(define make-ellipsis
(record-constructor ellipsis-type '(SIDS)))
(define ellipsis-sids
(record-accessor ellipsis-type 'SIDS))
(define set-ellipsis-sids!
(record-modifier ellipsis-type 'SIDS))