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add support for variable transformers: settable identifier syntax

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* module/ice-9/psyntax.scm (set!): Handle variable transformers; though,
  they cannot produce definitions.
  (make-variable-transformer): New procedure.
  (identifier-syntax): Allow the R6RS form that makes variable
  transformers.

* module/ice-9/psyntax-pp.scm: Regenerated.

* doc/ref/r6rs.texi (R6RS Incompatibilities): Remove letrec* item, and
  add set! restriction.
This commit is contained in:
Andy Wingo 2010-06-19 12:43:40 +02:00
commit bfccdcd530
3 changed files with 8296 additions and 7755 deletions
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38
module/ice-9/psyntax.scm
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@ -1327,7 +1327,6 @@
;; possible.
(define chi-macro
(lambda (p e r w s rib mod)
;; p := (procedure . module-name)
(define rebuild-macro-output
(lambda (x m)
(cond ((pair? x)
@ -2138,16 +2137,23 @@
(syntax-case e ()
((_ id val)
(id? #'id)
(let ((val (chi #'val r w mod))
(n (id-var-name #'id w)))
(let ((n (id-var-name #'id w)))
(let ((b (lookup n r mod)))
(case (binding-type b)
((lexical)
(build-lexical-assignment s
(syntax->datum #'id)
(binding-value b)
val))
((global) (build-global-assignment s n val mod))
(chi #'val r w mod)))
((global)
(build-global-assignment s n (chi #'val r w mod) mod))
((macro)
(let ((p (binding-value b)))
(if (procedure-property p 'variable-transformer)
(chi (chi-macro p e r w s #f mod) r w mod)
(syntax-violation 'set! "not a variable transformer"
(wrap e w mod)
(wrap #'id w mod)))))
((displaced-lexical)
(syntax-violation 'set! "identifier out of context"
(wrap #'id w mod)))
@ -2826,9 +2832,18 @@
clause))))))))
#'(let ((t e)) body))))))
(define (make-variable-transformer proc)
(if (procedure? proc)
(let ((trans (lambda (x)
#((macro-type . variable-transformer))
(proc x))))
(set-procedure-property! trans 'variable-transformer #t)
trans)
(error "variable transformer not a procedure" proc)))
(define-syntax identifier-syntax
(lambda (x)
(syntax-case x ()
(syntax-case x (set!)
((_ e)
#'(lambda (x)
#((macro-type . identifier-syntax))
@ -2837,7 +2852,16 @@
(identifier? #'id)
#'e)
((_ x (... ...))
#'(e x (... ...)))))))))
#'(e x (... ...))))))
((_ (id exp1) ((set! var val) exp2))
(and (identifier? #'id) (identifier? #'var))
#'(make-variable-transformer
(lambda (x)
#((macro-type . variable-transformer))
(syntax-case x (set!)
((set! var val) #'exp2)
((id x (... ...)) #'(exp1 x (... ...)))
(id (identifier? #'id) #'exp1))))))))
(define-syntax define*
(lambda (x)