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;"mwdenote.scm" Syntactic Environments
; Copyright 1992 William Clinger
;
; Permission to copy this software, in whole or in part, to use this
; software for any lawful purpose, and to redistribute this software
; is granted subject to the restriction that all copies made of this
; software must include this copyright notice in full.
;
; I also request that you send me a copy of any improvements that you
; make to this software so that they may be incorporated within it to
; the benefit of the Scheme community.
;;;; Syntactic environments.
; A syntactic environment maps identifiers to denotations,
; where a denotation is one of
;
; (special <special>)
; (macro <rules> <env>)
; (identifier <id>)
;
; and where <special> is one of
;
; quote
; lambda
; if
; set!
; begin
; define
; define-syntax
; let-syntax
; letrec-syntax
; syntax-rules
;
; and where <rules> is a compiled <transformer spec> (see R4RS),
; <env> is a syntactic environment, and <id> is an identifier.
(define mw:standard-syntax-environment
'((quote . (special quote))
(lambda . (special lambda))
(if . (special if))
(set! . (special set!))
(begin . (special begin))
(define . (special define))
(case . (special case)) ;; @@ added wdc
(let . (special let)) ;; @@ added KAD
(let* . (special let*)) ;; @@ "
(letrec . (special letrec)) ;; @@ "
(quasiquote . (special quasiquote)) ;; @@ "
(unquote . (special unquote)) ;; @@ "
(unquote-splicing . (special unquote-splicing)) ; @@ "
(do . (special do)) ;; @@ "
(define-syntax . (special define-syntax))
(let-syntax . (special let-syntax))
(letrec-syntax . (special letrec-syntax))
(syntax-rules . (special syntax-rules))
(... . (identifier ...))
(::: . (identifier :::))))
; An unforgeable synonym for lambda, used to expand definitions.
(define mw:lambda0 (string->symbol " lambda "))
; The mw:global-syntax-environment will always be a nonempty
; association list since there is no way to remove the entry
; for mw:lambda0. That entry is used as a header by destructive
; operations.
(define mw:global-syntax-environment
(cons (cons mw:lambda0
(cdr (assq 'lambda mw:standard-syntax-environment)))
(mw:syntax-copy mw:standard-syntax-environment)))
(define (mw:global-syntax-environment-set! env)
(set-cdr! mw:global-syntax-environment env))
(define (mw:syntax-bind-globally! id denotation)
(if (and (mw:identifier? denotation)
(eq? id (mw:identifier-name denotation)))
(letrec ((remove-bindings-for-id
(lambda (bindings)
(cond ((null? bindings) '())
((eq? (caar bindings) id)
(remove-bindings-for-id (cdr bindings)))
(else (cons (car bindings)
(remove-bindings-for-id (cdr bindings))))))))
(mw:global-syntax-environment-set!
(remove-bindings-for-id (cdr mw:global-syntax-environment))))
(let ((x (assq id mw:global-syntax-environment)))
(if x
(set-cdr! x denotation)
(mw:global-syntax-environment-set!
(cons (cons id denotation)
(cdr mw:global-syntax-environment)))))))
(define (mw:syntax-divert env1 env2)
(append env2 env1))
(define (mw:syntax-extend env ids denotations)
(mw:syntax-divert env (map cons ids denotations)))
(define (mw:syntax-lookup-raw env id)
(let ((entry (assq id env)))
(if entry
(cdr entry)
#f)))
(define (mw:syntax-lookup env id)
(or (mw:syntax-lookup-raw env id)
(mw:make-identifier-denotation id)))
(define (mw:syntax-assign! env id denotation)
(let ((entry (assq id env)))
(if entry
(set-cdr! entry denotation)
(mw:bug "Bug detected in mw:syntax-assign!" env id denotation))))
(define mw:denote-of-quote
(mw:syntax-lookup mw:standard-syntax-environment 'quote))
(define mw:denote-of-lambda
(mw:syntax-lookup mw:standard-syntax-environment 'lambda))
(define mw:denote-of-if
(mw:syntax-lookup mw:standard-syntax-environment 'if))
(define mw:denote-of-set!
(mw:syntax-lookup mw:standard-syntax-environment 'set!))
(define mw:denote-of-begin
(mw:syntax-lookup mw:standard-syntax-environment 'begin))
(define mw:denote-of-define
(mw:syntax-lookup mw:standard-syntax-environment 'define))
(define mw:denote-of-define-syntax
(mw:syntax-lookup mw:standard-syntax-environment 'define-syntax))
(define mw:denote-of-let-syntax
(mw:syntax-lookup mw:standard-syntax-environment 'let-syntax))
(define mw:denote-of-letrec-syntax
(mw:syntax-lookup mw:standard-syntax-environment 'letrec-syntax))
(define mw:denote-of-syntax-rules
(mw:syntax-lookup mw:standard-syntax-environment 'syntax-rules))
(define mw:denote-of-...
(mw:syntax-lookup mw:standard-syntax-environment '...))
(define mw:denote-of-:::
(mw:syntax-lookup mw:standard-syntax-environment ':::))
(define mw:denote-of-case
(mw:syntax-lookup mw:standard-syntax-environment 'case)) ;; @@ wdc
(define mw:denote-of-let
(mw:syntax-lookup mw:standard-syntax-environment 'let)) ;; @@ KenD
(define mw:denote-of-let*
(mw:syntax-lookup mw:standard-syntax-environment 'let*)) ;; @@ KenD
(define mw:denote-of-letrec
(mw:syntax-lookup mw:standard-syntax-environment 'letrec)) ;; @@ KenD
(define mw:denote-of-quasiquote
(mw:syntax-lookup mw:standard-syntax-environment 'quasiquote)) ;; @@ KenD
(define mw:denote-of-unquote
(mw:syntax-lookup mw:standard-syntax-environment 'unquote)) ;; @@ KenD
(define mw:denote-of-unquote-splicing
(mw:syntax-lookup mw:standard-syntax-environment 'unquote-splicing)) ;@@ KenD
(define mw:denote-of-do
(mw:syntax-lookup mw:standard-syntax-environment 'do)) ;; @@ KenD
(define mw:denote-class car)
;(define (mw:special? denotation)
; (eq? (mw:denote-class denotation) 'special))
;(define (mw:macro? denotation)
; (eq? (mw:denote-class denotation) 'macro))
(define (mw:identifier? denotation)
(eq? (mw:denote-class denotation) 'identifier))
(define (mw:make-identifier-denotation id)
(list 'identifier id))
(define macwork:rules cadr)
(define macwork:env caddr)
(define mw:identifier-name cadr)
(define (mw:same-denotation? d1 d2)
(or (eq? d1 d2)
(and (mw:identifier? d1)
(mw:identifier? d2)
(eq? (mw:identifier-name d1)
(mw:identifier-name d2)))))
; Renaming of variables.
; Given a datum, strips the suffixes from any symbols that appear within
; the datum, trying not to copy any more of the datum than necessary.
; @@ rewrote to strip *all* suffixes -- wdc
(define mw:strip
(letrec ((original-symbol
(lambda (x)
(let ((s (symbol->string x)))
(loop x s 0 (string-length s)))))
(loop
(lambda (sym s i n)
(cond ((= i n) sym)
((char=? (string-ref s i)
mw:suffix-character)
(string->symbol (substring s 0 i)))
(else
(loop sym s (+ i 1) n))))))
(lambda (x)
(cond ((symbol? x)
(original-symbol x))
((pair? x)
(let ((y (mw:strip (car x)))
(z (mw:strip (cdr x))))
(if (and (eq? y (car x))
(eq? z (cdr x)))
x
(cons y z))))
((vector? x)
(list->vector (map mw:strip (vector->list x))))
(else x)))))
; Given a list of identifiers, returns an alist that associates each
; identifier with a fresh identifier.
(define (mw:rename-vars vars)
(set! mw:renaming-counter (+ mw:renaming-counter 1))
(let ((suffix (string-append (string mw:suffix-character)
(number->string mw:renaming-counter))))
(map (lambda (var)
(if (symbol? var)
(cons var
(string->symbol
(string-append (symbol->string var) suffix)))
(slib:error "Illegal variable" var)))
vars)))
; Given a syntactic environment env to be extended, an alist returned
; by mw:rename-vars, and a syntactic environment env2, extends env by
; binding the fresh identifiers to the denotations of the original
; identifiers in env2.
(define (mw:syntax-alias env alist env2)
(mw:syntax-divert
env
(map (lambda (name-pair)
(let ((old-name (car name-pair))
(new-name (cdr name-pair)))
(cons new-name
(mw:syntax-lookup env2 old-name))))
alist)))
; Given a syntactic environment and an alist returned by mw:rename-vars,
; extends the environment by binding the old identifiers to the fresh
; identifiers.
(define (mw:syntax-rename env alist)
(mw:syntax-divert env
(map (lambda (old new)
(cons old (mw:make-identifier-denotation new)))
(map car alist)
(map cdr alist))))
; Given a <formals> and an alist returned by mw:rename-vars that contains
; a new name for each formal identifier in <formals>, renames the
; formal identifiers.
(define (mw:rename-formals formals alist)
(cond ((null? formals) '())
((pair? formals)
(cons (cdr (assq (car formals) alist))
(mw:rename-formals (cdr formals) alist)))
(else (cdr (assq formals alist)))))
(define mw:renaming-counter 0)
|