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|
;;;============================================================================
;;; File: "_syntax-template.scm"
;;; Copyright (c) 2000-2015 by Marc Feeley, All Rights Reserved.
;;;============================================================================
;; This file implements basic template expansion functionnality that is
;; used in the implementation of syntax definition forms (both
;; syntax-rules and syntax-case). It implements:
;;
;; - a compiler for syntax templates
;; - a syntax template expander
;; This file is typically used inside a macro definition body using an
;; (include "~~lib/_syntax-template.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 templates.
(define-macro (syn#template-list) -1)
(define-macro (syn#template-vect) -2)
(define-macro (syn#template-improper-list) -3)
(define-macro (syn#template-other) -4)
(define-macro (syn#template-repetition) -5)
;;;----------------------------------------------------------------------------
;; Syntax template compilation.
;; Compiled templates are represented as follows:
;;
;; Template Compiled template
;; <pattern variable> #(INDEX RANK) INDEX and RANK >= 0
;; (T1 T2 T3) #((syn#template-list) LOC CT1 CT2 CT3)
;; #(T1 T2 T3) #((syn#template-vect) LOC CT1 CT2 CT3)
;; (T1 T2 . T3) #((syn#template-improper-list) LOC CT1 CT2 CT3)
;; <other> #((syn#template-other) LOC <other>)
;; T ... #((syn#template-repetition) CT INDEX1 RANK1 INDEX2 RANK2 INDEX3 RANK3)
(define (syn#template-pvar? ctemplate)
(and (vector? ctemplate)
(let ((index (vector-ref ctemplate 0)))
(and (>= index 0) index))))
(define (syn#template-ellipsis? src)
(let ((code (##source-code src)))
(eq? code '...)))
(define (syn#ct-list template code pvars loop-nests tag-offs)
(let loop ((lst code)
(rev-ctemplate '()))
(cond ((pair? lst)
(let ((first (##sourcify (car lst) template))
(rest (cdr lst)))
(if (and (pair? rest)
(syn#template-ellipsis? (##sourcify (car rest) template)))
(let* ((loop-control
(vector '()))
(ctemplate
(syn#ct
first
pvars
(cons loop-control loop-nests)))
(x
(vector-ref loop-control 0)))
(if (null? x) ; is this loop nest unconstrained?
(error "iterated template is unconstrained")
(loop (cdr rest)
(cons (list->vector
(cons (syn#template-repetition) (cons ctemplate x)))
rev-ctemplate))))
(let ((ctemplate
(syn#ct
first
pvars
loop-nests)))
(loop rest
(cons ctemplate rev-ctemplate))))))
((null? lst)
(list->vector
(cons (+ (syn#template-list) tag-offs)
(cons (##source-locat template)
(reverse rev-ctemplate)))))
(else
(let ((ctemplate
(syn#ct
(##sourcify lst template)
pvars
loop-nests)))
(list->vector
(cons (syn#template-improper-list)
(cons (##source-locat template)
(reverse (cons ctemplate rev-ctemplate))))))))))
(define (syn#ct template pvars loop-nests)
(let ((code (##source-code template)))
(define (add-constraints! var-index n nests)
(cond ((= n 0))
((pair? nests)
(vector-set! (car nests) 0
(cons var-index
(cons (- n 1)
(vector-ref (car nests) 0))))
(add-constraints! var-index (- n 1) (cdr nests)))
(else
(error "insufficient nesting of pattern variable in template"))))
(define (handle-symbol sym)
(let ((x (assq sym pvars)))
(if x
(let ((var-index (cadr x))
(var-rank (cddr x)))
(add-constraints! var-index var-rank loop-nests)
(vector var-index
var-rank))
(handle-constant sym))))
(define (handle-constant const)
(vector (syn#template-other) ; const is not structured so desourcify not needed
(##source-locat template)
const))
(cond ((pair? code)
(if (and (syn#template-ellipsis? (##sourcify (car code) template))
(let ((rest (cdr code)))
(and (pair? rest)
(syn#template-ellipsis? (##sourcify (car rest) template))
(null? (cdr rest)))))
(handle-symbol '...)
(syn#ct-list
template
code
pvars
loop-nests
0)))
((vector? code)
(syn#ct-list
template
(vector->list code)
pvars
loop-nests
-1))
((symbol? code)
(if (eq? code '...)
(error "improperly placed ellipsis in pattern")
(handle-symbol code)))
(else
(handle-constant code)))))
(define (syn#compile-template template pattern-vars)
(syn#ct
template
pattern-vars
'()))
;;;----------------------------------------------------------------------------
;; Syntax template expansion.
(define (syn#et ctemplate bindings loop-nests tail)
(define (fetch rank nests binding)
(if (= rank 0)
binding
(vector-ref (fetch (- rank 1) (cdr nests) binding)
(car nests))))
(define (size i)
(vector-length
(fetch (vector-ref ctemplate (- i 1))
loop-nests
(vector-ref bindings (vector-ref ctemplate (- i 2))))))
(define (build-list i t)
(if (< i 2)
t
(build-list (- i 1)
(syn#et
(vector-ref ctemplate i)
bindings
loop-nests
t))))
(let ((tag (vector-ref ctemplate 0))
(len (vector-length ctemplate)))
(cond ((= tag (syn#template-list))
(cons (##make-source
(build-list (- len 1) '())
(vector-ref ctemplate 1))
tail))
((= tag (syn#template-vect))
(cons (##make-source
(list->vector (build-list (- len 1) '()))
(vector-ref ctemplate 1))
tail))
((= tag (syn#template-improper-list))
(cons (##make-source
(build-list (- len 2)
(let ((t (car (syn#et
(vector-ref ctemplate (- len 1))
bindings
loop-nests
'()))))
(if (##source? t)
(##source-code t)
t)))
(vector-ref ctemplate 1))
tail))
((= tag (syn#template-other))
(cons (##make-source
(vector-ref ctemplate 2)
(vector-ref ctemplate 1))
tail))
((= tag (syn#template-repetition))
(let ((n (size len)))
(let loop1 ((i (- len 2)))
(if (< i 3)
(let loop2 ((j (- n 1))
(t tail))
(if (< j 0)
t
(loop2 (- j 1)
(syn#et
(vector-ref ctemplate 1)
bindings
(cons j loop-nests)
t))))
(if (= n (size i))
(loop1 (- i 2))
(error "inconsistent loop"))))))
(else
;; template is a pattern variable
(let ((var-index tag)
(var-rank (vector-ref ctemplate 1)))
(cons (fetch var-rank
loop-nests
(vector-ref bindings var-index))
tail))))))
(define (syn#expand-template ctemplate bindings)
(car (syn#et
ctemplate
bindings
'()
'())))
;;;============================================================================
|
