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|
;;;============================================================================
;;; File: "_syntax-pattern.scm"
;;; Copyright (c) 2000-2015 by Marc Feeley, All Rights Reserved.
;;;============================================================================
;; This file implements basic pattern matching functionnality that is
;; used in the implementation of syntax definition forms (both
;; syntax-rules and syntax-case). It implements:
;;
;; - a compiler for syntax patterns
;; - a syntax pattern matcher
;; This file is typically used inside a macro definition body using an
;; (include "~~lib/_syntax-pattern.scm") so the toplevel definitions
;; in this file are actually local definitions of the enclosing macro
;; definition. Nevertheless, all toplevel definitions define identifiers
;; that are prefixed with the "syn#" namespace.
;;;----------------------------------------------------------------------------
;; Define encoding of compiled patterns.
(define-macro (syn#pattern-var) 0)
(define-macro (syn#pattern-underscore) -1)
(define-macro (syn#pattern-fixed-list) -2)
(define-macro (syn#pattern-fixed-vect) -3)
(define-macro (syn#pattern-tail-list) -4)
(define-macro (syn#pattern-tail-vect) -5)
(define-macro (syn#pattern-improper-list) -6)
;;;----------------------------------------------------------------------------
;; Syntax pattern compilation.
;; Compiled patterns are represented as follows:
;;
;; Pattern Compiled pattern
;; <pattern variable> #((syn#pattern-var))
;; _ #((syn#pattern-underscore))
;; (P1 P2 P3) #((syn#pattern-fixed-list) CP1 CP2 CP3)
;; #(P1 P2 P3) #((syn#pattern-fixed-vect) CP1 CP2 CP3)
;; (P1 P2 P3 ...) #((syn#pattern-tail-list) CP1 CP2 CP3)
;; #(P1 P2 P3 ...) #((syn#pattern-tail-vect) CP1 CP2 CP3)
;; (P1 P2 . P3) #((syn#pattern-improper-list) CP1 CP2 CP3)
;; <other> <other> note: can't be a list or vector
(define (syn#pattern-pvar? cpattern)
(and (vector? cpattern)
(let ((tag (vector-ref cpattern 0)))
(= tag (syn#pattern-var)))))
(define (syn#pattern-ellipsis? src)
(let ((code (##source-code src)))
(eq? code '...)))
(define (syn#cp-list pattern code literals pattern-vars rank tag-offs cont)
(let loop ((lst code)
(rev-cpattern '())
(new-pattern-vars pattern-vars))
(cond ((pair? lst)
(let ((first (##sourcify (car lst) pattern))
(rest (cdr lst)))
(if (and (pair? rest)
(null? (cdr rest))
(syn#pattern-ellipsis? (##sourcify (car rest) pattern)))
(syn#cp
first
literals
new-pattern-vars
(+ rank 1)
(lambda (cpattern pvars)
(cont (list->vector
(cons (+ (syn#pattern-tail-list) tag-offs)
(reverse (cons cpattern rev-cpattern))))
pvars)))
(syn#cp
first
literals
new-pattern-vars
rank
(lambda (cpattern pvars)
(loop rest
(cons cpattern rev-cpattern)
pvars))))))
((null? lst)
(cont (list->vector
(cons (+ (syn#pattern-fixed-list) tag-offs)
(reverse rev-cpattern)))
new-pattern-vars))
(else
(syn#cp
(##sourcify lst pattern)
literals
new-pattern-vars
rank
(lambda (cpattern pvars)
(cont (list->vector
(cons (syn#pattern-improper-list)
(reverse (cons cpattern rev-cpattern))))
pvars)))))))
(define (syn#cp pattern literals pattern-vars rank cont)
(let ((code (##source-code pattern)))
(define (handle-symbol sym)
(cond ((memq sym literals)
(handle-constant sym))
((eq? sym '_)
(cont (vector (syn#pattern-underscore))
pattern-vars))
(else
(let ((x (assq sym pattern-vars)))
(if x
(error "duplicate pattern variable")
(let ((index (length pattern-vars)))
(cont (vector (syn#pattern-var)) ;; TODO: replace with '#(0) to allow sharing?
(cons (cons sym (cons index rank))
pattern-vars))))))))
(define (handle-constant const)
(cont const ; const is not structured so desourcify not needed
pattern-vars))
(cond ((pair? code)
(if (and (syn#pattern-ellipsis? (##sourcify (car code) pattern))
(let ((rest (cdr code)))
(and (pair? rest)
(syn#pattern-ellipsis? (##sourcify (car rest) pattern))
(null? (cdr rest)))))
(handle-symbol '...)
(syn#cp-list
pattern
code
literals
pattern-vars
rank
0
cont)))
((vector? code)
(syn#cp-list
pattern
(vector->list code)
literals
pattern-vars
rank
-1
cont))
((symbol? code)
(if (eq? code '...)
(error "improperly placed ellipsis in pattern")
(handle-symbol code)))
(else
(handle-constant code)))))
(define (syn#compile-pattern pattern literals cont)
(syn#cp
pattern
literals
'()
0
(lambda (cpattern pvars)
(cont cpattern
(reverse pvars)))))
;;;----------------------------------------------------------------------------
;; Syntax pattern matching.
(define (syn#match-success? x) ;; external representation of success is vector
(vector? x))
(define (syn#fail? x) ;; internal representation of failure is vector
(vector? x))
(define (syn#match-fail input msg . args)
(list->vector (cons input (cons msg args))))
(define (syn#mp-list cpattern input code bindings)
(let loop1 ((i 1)
(lst code)
(bs bindings))
(define (match-empty cpattern bindings)
(if (vector? cpattern)
;; all the pattern variables in cpattern must get bound to
;; the empty sequence
(let ((tag (vector-ref cpattern 0)))
(if (< tag (syn#pattern-underscore))
(let loop ((i 1)
(bs bindings))
(if (< i (vector-length cpattern))
(loop (+ i 1)
(match-empty (vector-ref cpattern i) bs))
bs))
(cons '#() bindings)))
bindings))
(define (match-next)
(if (not (pair? lst))
(syn#match-fail input "form is too short")
(let* ((sub-cpattern
(vector-ref cpattern i))
(next
(##sourcify (car lst) input))
(new-bs
(syn#mp
sub-cpattern
next
bs)))
(if (syn#fail? new-bs)
new-bs
(loop1 (+ i 1)
(cdr lst)
new-bs)))))
(if (< i (- (vector-length cpattern) 1))
(match-next)
(let ((tag (vector-ref cpattern 0)))
(if (< (syn#pattern-tail-list) tag)
;; list or vector pattern with no ellipsis or tail pattern
(if (< i (vector-length cpattern))
(match-next)
(if (not (null? lst))
(syn#match-fail input "form is too long")
bs))
(let ((sub-cpattern (vector-ref cpattern i)))
(if (< (syn#pattern-improper-list) tag)
;; list or vector pattern with ellipsis
(if (null? lst) ;; repetition factor is zero?
(match-empty sub-cpattern bs)
(let loop2 ((lst lst)
(local-bs '()))
(define (spread lst1 lst2)
(if (pair? lst1)
(if (pair? lst2)
(cons (cons (car lst1) (car lst2))
(spread (cdr lst1) (cdr lst2)))
(cons (list (car lst1))
(spread (cdr lst1) lst2)))
'()))
(define (combine lst1 lst2)
(if (pair? lst1)
(cons (list->vector (reverse (car lst1)))
(combine (cdr lst1) lst2))
lst2))
(cond ((pair? lst)
(let ((x
(syn#mp
sub-cpattern
(##sourcify (car lst) input)
'())))
(if (syn#fail? x)
x
(loop2 (cdr lst)
(spread x local-bs)))))
((null? lst)
(combine local-bs bs))
(else
#f))))
;; tail pattern of a list pattern
(syn#mp
sub-cpattern
(if (##source? lst)
lst
(##sourcify-aux1 lst input))
bs))))))))
(define (syn#mp cpattern input bindings)
(let ((code (##source-code input)))
(if (not (vector? cpattern))
(if (not (equal? cpattern ;; cpattern is not a list or vector so
code)) ;; desourcify not needed
(syn#match-fail input "expected:" cpattern)
bindings)
(let ((tag (vector-ref cpattern 0)))
(cond ((or (= tag (syn#pattern-fixed-vect))
(= tag (syn#pattern-tail-vect)))
;; input has to be a vector
(if (not (vector? code))
(syn#match-fail input "vector expected")
(syn#mp-list
cpattern
input
(vector->list code)
bindings)))
((< tag (syn#pattern-underscore))
;; input has to be a list
(if (not (or (pair? code)
(null? code)))
(syn#match-fail input "list expected")
(syn#mp-list
cpattern
input
code
bindings)))
((= tag (syn#pattern-underscore))
;; input can be anything
bindings)
(else
(cons input bindings)))))))
(define (syn#match-pattern cpattern input)
(let ((bindings (syn#mp cpattern input '())))
(if (syn#fail? bindings)
(vector->list bindings)
(list->vector (reverse bindings)))))
;;;============================================================================
|
