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;; Copyright (C) 1997, 1998 Free Software Foundation, Inc.
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this software; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
;;
;; As a special exception, the Free Software Foundation gives permission
;; for additional uses of the text contained in its release of GUILE.
;;
;; The exception is that, if you link the GUILE library with other files
;; to produce an executable, this does not by itself cause the
;; resulting executable to be covered by the GNU General Public License.
;; Your use of that executable is in no way restricted on account of
;; linking the GUILE library code into it.
;;
;; This exception does not however invalidate any other reasons why
;; the executable file might be covered by the GNU General Public License.
;;
;; This exception applies only to the code released by the
;; Free Software Foundation under the name GUILE.  If you copy
;; code from other Free Software Foundation releases into a copy of
;; GUILE, as the General Public License permits, the exception does
;; not apply to the code that you add in this way.  To avoid misleading
;; anyone as to the status of such modified files, you must delete
;; this exception notice from them.
;;
;; If you write modifications of your own for GUILE, it is your choice
;; whether to permit this exception to apply to your modifications.
;; If you do not wish that, delete this exception notice.

;;;; "Macro.scm", Support for syntax-rules macros.
;;; Author: Radey Shouman
;;
;; As in SYNTAX-CASE, the identifier ... may be quoted in a 
;; SYNTAX-RULES pattern or template as (... ...).
;;
;; THE-MACRO may be used to define macros, eg
;; (define-syntax foo (the-macro and))
;; defines the syntactic keyword FOO to have the same transformer 
;; as the macro AND.

(require 'rev2-procedures) ;append!
(require 'record)

(define macro:compile-syntax-rules
  ;; We keep local copies of these standard special forms, otherwise, 
  ;; redefining them before they are memoized below can lead to 
  ;; infinite recursion.
  (@let-syntax ((lambda (the-macro lambda))
		(let (the-macro let))
		(cond (the-macro cond))
		(if (the-macro if))
		(and (the-macro and))
		(or (the-macro or)))
    (let ((var-rtd (make-record-type '? '(name rank)))
	  (e-pat-rtd (make-record-type '... '(pattern vars))))
      
      (define pattern-variable (record-constructor var-rtd '(name rank)))
      (define pattern-variable? (record-predicate var-rtd))
      (define pattern-variable->name
	(let ((acc (record-accessor var-rtd 'name)))
	  (lambda (x) (identifier->symbol (acc x)))))
      (define pattern-variable->rank (record-accessor var-rtd 'rank))

      ;; An ellipsis-pattern is used both for ellipses in patterns and
      ;; ellipses in templates.  In a pattern, VARS is the list of variables
      ;; bound by the ellipsis pattern.  In a template, VARS is the list of
      ;; variables opened by the ellipsis template.

      (define ellipsis-pattern (record-constructor e-pat-rtd '(pattern vars)))
      (define ellipsis-pattern? (record-predicate e-pat-rtd))
      (define ellipsis-pattern->pattern (record-accessor e-pat-rtd 'pattern))
      (define ellipsis-pattern->vars (record-accessor e-pat-rtd 'vars))

      (define (append2 x y)
	(if (null? y) x
	    (append x y)))
      
      (define ellipsis?
	(let (($... (renamed-identifier '... #f)))
	  (lambda (x env)
	    (and
	     (identifier? x)
	     (identifier-equal? x $... env)))))

      ;; Yeah, it's quadratically slow.
      (define (duplicates? vars)
	(if (null? vars)
	    #f
	    (if (memq (car vars) (cdr vars))
		(car vars)
		(duplicates? (cdr vars)))))

      (define (compile-pattern literals rule env-def)
	(let recur ((pat (cdar rule))
		    (vars '())
		    (rank 0)
		    (k (lambda (compiled vars)
			 (let ((dup (duplicates? (map car vars))))
			   (if dup
			       (error 
				"syntax-rules: duplicate pattern variable:"
				dup " in rule " rule)))
			 (cons compiled
			       (rewrite-template
				(cadr rule) vars env-def)))))
	  (cond ((null? pat)
		 (k pat vars))
		((identifier? pat)
		 (let ((lit (memq pat literals)))
		   (if lit
		       (k pat vars)
		       (let ((var (pattern-variable pat rank)))
			 (k var (cons (cons pat var) vars))))))
		((pair? pat)
		 (if (and (pair? (cdr pat))
			  (ellipsis? (cadr pat) env-def)
			  (or (null? (cddr pat))
			      (error "bad ellipsis:" pat)))
		     (if (ellipsis? (car pat) env-def)
			 (recur (car pat) vars rank k)
			 (recur (car pat) '() (+ rank 1)
				(lambda (comp1 vars1)
				  (k (list
				      (ellipsis-pattern comp1 (map cdr vars1)))
				     (append2 vars1 vars)))))
		     (recur (car pat) '() rank
			    (lambda (comp1 vars1)
			      (recur (cdr pat) vars rank
				     (lambda (comp2 vars2)
				       (k (cons comp1 comp2)
					  (append2 vars1 vars2))))))))
		((vector? pat)
		 (recur (vector->list pat) vars rank
			(lambda (comp vars)
			  (k (list->vector comp) vars))))
		(else
		 (k pat vars)))))
      
      (define (rewrite-template template vars env-def)
	(let recur ((tmpl template)
		    (rank 0)
		    (inserted '())
		    (k (lambda (compiled inserted opened)
			 (list inserted compiled))))
	  (cond ((null? tmpl)
		 (k tmpl '() '()))
		((identifier? tmpl)
		 (let ((v (assq tmpl vars)))
		   (if v
		       (cond ((= rank (pattern-variable->rank (cdr v)))
			      (k (cdr v) '() (list (cdr v))))
			     ((> rank (pattern-variable->rank (cdr v)))
			      (k (cdr v) '() '()))
			     (else
			      (error "pattern variable rank mismatch:" tmpl
				     " in " template)))
		       (k tmpl (list tmpl) '()))))
		((pair? tmpl)
		 (if (and (pair? (cdr tmpl))
			  (ellipsis? (cadr tmpl) env-def))
		     (if (and (ellipsis? (car tmpl) env-def)
			      (or (null? (cddr tmpl))
				  (error "bad ellipsis:" tmpl)))
			 ;; (... ...) escape
			 (k (car tmpl) (list (car tmpl)) '()) 
			 (recur (car tmpl) (+ rank 1) '()
				(lambda (comp1 ins1 op1)
				  (if (null? op1)
				      (error "Bad ellipsis:"
					     tmpl " in template " template))
				  (recur (cddr tmpl) rank inserted
					 (lambda (comp2 ins2 op2)
					   (k (cons
					       (ellipsis-pattern comp1 op1)
					       comp2)
					      (append2 ins1 ins2)
					      (append2 op1 op2)))))))
		     (recur (car tmpl) rank '()
			    (lambda (comp1 ins1 op1)
			      (recur (cdr tmpl) rank inserted
				     (lambda (comp2 ins2 op2)
				       (k (cons comp1 comp2)
					  (append2 ins1 ins2)
					  (append2 op1 op2))))))))
		((vector? tmpl)
		 (recur (vector->list tmpl) rank inserted
			(lambda (compiled inserted opened)
			  (k (list->vector compiled) inserted opened))))
		(else
		 (k tmpl '() '())))))


;;; Match EXP to RULE, returning alist of variable bindings or #f.

      (define (match literals rule exp env-def env-use)
	(let recur ((r rule)
		    (x (cdr exp)))
	  (cond ((null? r)
		 (and (null? x) '()))
		((pair? r)
		 (if (ellipsis-pattern? (car r))
		     (and 
		      (list? x)
		      (let ((pat (ellipsis-pattern->pattern (car r))))
			(let match1 ((x x)
				     (vals '()))
			  (if (null? x)
			      (if (null? vals)
				  (map list (ellipsis-pattern->vars (car r)))
				  (let ((vars (map car (car vals))))
				    (apply map list vars
					   (map (lambda (al)
						  (map cdr al))
						(reverse vals)))))
			      (let ((val (recur pat (car x))))
				(and val
				     (match1 (cdr x) (cons val vals))))))))
		     (and
		      (pair? x)
		      (let ((v1 (recur (car r) (car x))))
			(and v1
			     (let ((v2 (recur (cdr r) (cdr x))))
			       (and v2 (append2 v1 v2))))))))
		((identifier? r)		;literal
		 (and (identifier? x)
		      (identifier-equal? (cdr (assq r literals)) x env-use)
		      '()))
		((pattern-variable? r)
		 (list (cons r x)))
		((vector? r)
		 (and (vector? x)
		      (recur (vector->list r) (vector->list x))))
		(else
		 (and (equal? r x) '())))))

      (define (substitute-in-template inserted template vars env-def)
	(let ((ins (map (lambda (id)
			  (cons id (renamed-identifier id env-def)))
			inserted)))
	  (let recur ((tmpl template)
		      (vars vars))
	    (cond ((null? tmpl)
		   tmpl)
		  ((pair? tmpl)
		   (if (ellipsis-pattern? (car tmpl))
		       (let ((enames (ellipsis-pattern->vars (car tmpl)))
			     (etmpl (ellipsis-pattern->pattern (car tmpl))))
			 (let ((evals (apply map list
					     (map (lambda (nam)
						    (cdr (assq nam vars)))
						  enames))))
			   (append!
			    (map (lambda (eval)
				   (recur etmpl
					  (append!
					   (map cons enames eval)
					   vars)))
				 evals)
			    (recur (cdr tmpl) vars))))
		       (cons (recur (car tmpl) vars)
			     (recur (cdr tmpl) vars))))
		  ((identifier? tmpl)
		   (let ((a (assq tmpl ins)))
		     (if a (cdr a) tmpl)))
		  ((pattern-variable? tmpl)
		   (@copy-tree (cdr (assq tmpl vars))))
		  ((vector? tmpl)
		   (list->vector (recur (vector->list tmpl) vars)))
		  (else
		   tmpl)))))

      ;; MACRO:COMPILE-SYNTAX-RULES
      (lambda (x-def env-def)
	(or (and (list? x-def)
		 (< 2 (length x-def))
		 (list? (cadr x-def)))
	    (error "Malformed syntax-rules:" x-def))
	(let ((literals (cadr x-def)))
	  (for-each (lambda (x)
		      (or (identifier? x)
			  (error "Bad literals list:" x-def)))
		    literals)

	  ;;Rules have the form: (<pattern> <inserted-identifiers> <template>).
	  (let ((rules 
		 (map
		  (lambda (rule)
		    (or (and (list? rule)
			     (= 2 (length rule)))
			(error "Bad rule:" rule))
		    (compile-pattern literals rule env-def))
		  (cddr x-def)))
		(re-lits
		 (map (lambda (sym)
			(cons sym (renamed-identifier sym env-def)))
		      literals)))
	    
	    (lambda (x-use env-use)
	      (let loop ((rules rules))
		(cond ((null? rules)
		       (error "macro use does not match definition:"
			      x-use))
		      ((match re-lits (caar rules) x-use env-def env-use) 
		       => (lambda (vars)
			    (let ((r (car rules)))
			      (substitute-in-template (cadr r) 
						      (caddr r)
						      vars
						      env-def))))
		      (else
		       (loop (cdr rules))))))))))))

(define syntax-rules
  (procedure->syntax
   (lambda (expr env-def)
     (procedure->memoizing-macro
      (macro:compile-syntax-rules expr env-def)))))

(define define-syntax
  (syntax-rules ()
    ((define-syntax ?name ?val)
     (define ?name (the-macro ?val)))))

(define-syntax let-syntax
  (syntax-rules () ((let-syntax ((?name ?val) ...) . ?body)
		    (@let-syntax
			((?name (the-macro ?val)) ...) . ?body))))

(define-syntax letrec-syntax
  (syntax-rules () ((letrec-syntax ((?name ?val) ...) . ?body)
		    (@letrec-syntax
		     ((?name (the-macro ?val)) ...) . ?body))))

;; MACRO:EXPAND would require substantial work.
(define macro:load load)
(define macro:eval eval)
(provide 'macro)