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syntax...

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This commit is contained in:
Jan Nieuwenhuizen 2016-10-18 22:19:57 +02:00
parent 44b26569a6
commit d53ea79a5d
2 changed files with 196 additions and 35 deletions
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3
GNUmakefile
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@ -44,3 +44,6 @@ boot: all
run: all
cat scm.mes test.mes | ./mes
syntax: all
cat scm.mes syntax.mes | ./mes

228
syntax.mes
View file

@ -1,21 +1,202 @@
;; (display "define-syntax...")
(display "define-syntax...")
;; (define-macro define-syntax
;; (lambda (form expander)
;; (expander `(define-macro ,(cadr form)
;; (let ((transformer ,(caddr form)))
;; (lambda (form expander)
;; (expander (transformer form
;; (lambda (x) x)
;; eq?)
;; expander))))
;; expander)))
(define-macro define-syntax
(lambda (form expander)
(expander `(define-macro ,(cadr form)
(let ((transformer ,(caddr form)))
(lambda (form expander)
(expander (transformer form
(lambda (x) x)
eq?)
expander))))
expander)))
(newline)
;; (newline)
(display "define-syntax when...")
(define-syntax syntax-rules
(let ()
(define name? symbol?)
(define (segment-pattern? pattern)
(and (segment-template? pattern)
(or (null? (cddr pattern))
(syntax-error "segment matching not implemented" pattern))))
(define (segment-template? pattern)
(and (pair? pattern)
(pair? (cdr pattern))
(memq (cadr pattern) indicators-for-zero-or-more)))
(define indicators-for-zero-or-more (list (string->symbol "...") '---))
(lambda (exp r c)
(define %input (r '%input)) ;Gensym these, if you like.
(define %compare (r '%compare))
(define %rename (r '%rename))
(define %tail (r '%tail))
(define %temp (r '%temp))
(define rules (cddr exp))
(define subkeywords (cadr exp))
(define (make-transformer rules)
`(lambda (,%input ,%rename ,%compare)
(let ((,%tail (cdr ,%input)))
(cond ,@(map process-rule rules)
(else
(syntax-error
"use of macro doesn't match definition"
,%input))))))
(define (process-rule rule)
(if (and (pair? rule)
(pair? (cdr rule))
(null? (cddr rule)))
(let ((pattern (cdar rule))
(template (cadr rule)))
`((and ,@(process-match %tail pattern))
(let* ,(process-pattern pattern
%tail
(lambda (x) x))
,(process-template template
0
(meta-variables pattern 0 '())))))
(syntax-error "ill-formed syntax rule" rule)))
; Generate code to test whether input expression matches pattern
(define (process-match input pattern)
(cond ((name? pattern)
(if (member pattern subkeywords)
`((,%compare ,input (,%rename ',pattern)))
`()))
((segment-pattern? pattern)
(process-segment-match input (car pattern)))
((pair? pattern)
`((let ((,%temp ,input))
(and (pair? ,%temp)
,@(process-match `(car ,%temp) (car pattern))
,@(process-match `(cdr ,%temp) (cdr pattern))))))
((or (null? pattern) (boolean? pattern) (char? pattern))
`((eq? ,input ',pattern)))
(else
`((equal? ,input ',pattern)))))
(define (process-segment-match input pattern)
(let ((conjuncts (process-match '(car l) pattern)))
(if (null? conjuncts)
`((list? ,input)) ;+++
`((let loop ((l ,input))
(or (null? l)
(and (pair? l)
,@conjuncts
(loop (cdr l)))))))))
; Generate code to take apart the input expression
; This is pretty bad, but it seems to work (can't say why).
(define (process-pattern pattern path mapit)
(cond ((name? pattern)
(if (memq pattern subkeywords)
'()
(list (list pattern (mapit path)))))
((segment-pattern? pattern)
(process-pattern (car pattern)
%temp
(lambda (x) ;temp is free in x
(mapit (if (eq? %temp x)
path ;+++
`(map (lambda (,%temp) ,x)
,path))))))
((pair? pattern)
(append (process-pattern (car pattern) `(car ,path) mapit)
(process-pattern (cdr pattern) `(cdr ,path) mapit)))
(else '())))
; Generate code to compose the output expression according to template
(define (process-template template rank env)
(cond ((name? template)
(let ((probe (assq template env)))
(if probe
(if (<= (cdr probe) rank)
template
(syntax-error "template rank error (too few ...'s?)"
template))
`(,%rename ',template))))
((segment-template? template)
(let ((vars
(free-meta-variables (car template) (+ rank 1) env '())))
(if (null? vars)
(syntax-error "too many ...'s" template)
(let* ((x (process-template (car template)
(+ rank 1)
env))
(gen (if (equal? (list x) vars)
x ;+++
`(map (lambda ,vars ,x)
,@vars))))
(if (null? (cddr template))
gen ;+++
`(append ,gen ,(process-template (cddr template)
rank env)))))))
((pair? template)
`(cons ,(process-template (car template) rank env)
,(process-template (cdr template) rank env)))
(else `(quote ,template))))
; Return an association list of (var . rank)
(define (meta-variables pattern rank vars)
(cond ((name? pattern)
(if (memq pattern subkeywords)
vars
(cons (cons pattern rank) vars)))
((segment-pattern? pattern)
(meta-variables (car pattern) (+ rank 1) vars))
((pair? pattern)
(meta-variables (car pattern) rank
(meta-variables (cdr pattern) rank vars)))
(else vars)))
; Return a list of meta-variables of given higher rank
(define (free-meta-variables template rank env free)
(cond ((name? template)
(if (and (not (memq template free))
(let ((probe (assq template env)))
(and probe (>= (cdr probe) rank))))
(cons template free)
free))
((segment-template? template)
(free-meta-variables (car template)
rank env
(free-meta-variables (cddr template)
rank env free)))
((pair? template)
(free-meta-variables (car template)
rank env
(free-meta-variables (cdr template)
rank env free)))
(else free)))
c ;ignored
;; Kludge for Scheme48 linker.
;; `(cons ,(make-transformer rules)
;; ',(find-free-names-in-syntax-rules subkeywords rules))
(make-transformer rules))))
;; (define-syntax when
;; (syntax-rules ()
;; ((when condition exp ...)
@ -29,27 +210,4 @@
;; (define-macro (when clause . rest)
;; (list 'cond (list clause (list 'let '() rest))))
(define-macro (when expr . body)
`(if ,expr
((lambda () ,@body))
'bah))
(newline)
(when #t
(display "true")
(newline))
(when #t
(display "q-when")
(newline)
'())
(define *gensym* 0)
(define (gensym)
(set! *gensym* (+ *gensym* 1))
(string->symbol (string-append "g" (number->string *gensym*))))
(newline)