#| -*-Scheme-*-

$Id: mit-syntax.scm,v 14.19 2003/04/17 02:52:08 cph Exp $

Copyright 1989,1990,1991,2001,2002,2003 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme 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 of the License, or (at
your option) any later version.

MIT/GNU Scheme 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 MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
USA.

|#

;;;; MIT/GNU Scheme Syntax

(declare (usual-integrations))

;;;; Macro transformers

(define (define-er-macro-transformer keyword environment transformer)
  (syntactic-environment/define environment keyword
    (er-macro-transformer->expander transformer environment)))

(define (transformer-keyword transformer->expander-name transformer->expander)
  (lambda (form environment definition-environment history)
    definition-environment		;ignore
    (syntax-check '(KEYWORD EXPRESSION) form history)
    (expression->keyword-value-item (classify/subexpression (cadr form)
							    environment
							    history
							    select-cadr)
				    environment
				    history
				    transformer->expander-name
				    transformer->expander)))

(define (expression->keyword-value-item item environment history
					transformer->expander-name
					transformer->expander)
  (make-keyword-value-item
   (transformer->expander
    (transformer-eval (compile-item/expression item)
		      (syntactic-environment->environment environment))
    environment)
   (make-expression-item history
     (lambda ()
       (output/combination
	(output/access-reference transformer->expander-name
				 system-global-environment)
	(list (compile-item/expression item)
	      (output/the-environment)))))))

(define-classifier 'SC-MACRO-TRANSFORMER system-global-environment
  ;; "Syntactic Closures" transformer
  (transformer-keyword 'SC-MACRO-TRANSFORMER->EXPANDER
		       sc-macro-transformer->expander))

(define-classifier 'RSC-MACRO-TRANSFORMER system-global-environment
  ;; "Reversed Syntactic Closures" transformer
  (transformer-keyword 'RSC-MACRO-TRANSFORMER->EXPANDER
		       rsc-macro-transformer->expander))

(define-classifier 'ER-MACRO-TRANSFORMER system-global-environment
  ;; "Explicit Renaming" transformer
  (transformer-keyword 'ER-MACRO-TRANSFORMER->EXPANDER
		       er-macro-transformer->expander))

(define-classifier 'NON-HYGIENIC-MACRO-TRANSFORMER system-global-environment
  (transformer-keyword 'NON-HYGIENIC-MACRO-TRANSFORMER->EXPANDER
		       non-hygienic-macro-transformer->expander))

;;;; Core primitives

(define-compiler 'LAMBDA system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD MIT-BVL + FORM) form history)
    (call-with-values
	(lambda ()
	  (compile/lambda (cadr form)
			  (cddr form)
			  select-cddr
			  environment
			  history))
      (lambda (bvl body)
	(output/lambda bvl body)))))

(define-compiler 'NAMED-LAMBDA system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD (IDENTIFIER . MIT-BVL) + FORM) form history)
    (call-with-values
	(lambda ()
	  (compile/lambda (cdadr form)
			  (cddr form)
			  select-cddr
			  environment
			  history))
      (lambda (bvl body)
	(output/named-lambda (identifier->symbol (caadr form)) bvl body)))))

(define (compile/lambda bvl body select-body environment history)
  (let ((environment (make-internal-syntactic-environment environment)))
    ;; Force order -- bind names before classifying body.
    (let ((bvl
	   (map-mit-lambda-list (lambda (identifier)
				  (bind-variable! environment identifier))
				bvl)))
      (values bvl
	      (compile-body-item
	       (classify/body body
			      environment
			      environment
			      history
			      select-body))))))

(define (map-mit-lambda-list procedure bvl)
  (let loop ((bvl bvl))
    (if (pair? bvl)
	(cons (if (or (eq? (car bvl) lambda-optional-tag)
		      (eq? (car bvl) lambda-rest-tag))
		  (car bvl)
		  (procedure (car bvl)))
	      (loop (cdr bvl)))
	(if (identifier? bvl)
	    (procedure bvl)
	    '()))))

(define-classifier 'BEGIN system-global-environment
  (lambda (form environment definition-environment history)
    (syntax-check '(KEYWORD * FORM) form history)
    (make-body-item history
		    (classify/subforms (cdr form)
				       environment
				       definition-environment
				       history
				       select-cdr))))

(define-compiler 'IF system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD EXPRESSION EXPRESSION ? EXPRESSION)
		  form history)
    (output/conditional
     (compile/subexpression (cadr form) environment history select-cadr)
     (compile/subexpression (caddr form) environment history select-caddr)
     (if (pair? (cdddr form))
	 (compile/subexpression (cadddr form)
				environment
				history
				select-cadddr)
	 (output/unspecific)))))

(define-compiler 'QUOTE system-global-environment
  (lambda (form environment history)
    environment			;ignore
    (syntax-check '(KEYWORD DATUM) form history)
    (output/constant (strip-syntactic-closures (cadr form)))))

(define-compiler 'SET! system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD FORM ? EXPRESSION) form history)
    (call-with-values
	(lambda ()
	  (classify/sublocation (cadr form) environment history select-cadr))
      (lambda (name environment-item)
	(let ((value
	       (if (pair? (cddr form))
		   (compile/subexpression (caddr form)
					  environment
					  history
					  select-caddr)
		   (output/unassigned))))
	  (if environment-item
	      (output/access-assignment
	       name
	       (compile-item/expression environment-item)
	       value)
	      (output/assignment name value)))))))

(define (classify/sublocation form environment history selector)
  (classify/location form
		     environment
		     (history/add-subproblem form
					     environment
					     history
					     selector)))

(define (classify/location form environment history)
  (let ((item (classify/expression form environment history)))
    (cond ((variable-item? item)
	   (values (variable-item/name item) #f))
	  ((access-item? item)
	   (values (access-item/name item) (access-item/environment item)))
	  (else
	   (syntax-error history "Variable required in this context:" form)))))

(define-compiler 'DELAY system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD EXPRESSION) form history)
    (output/delay
     (compile/subexpression (cadr form)
			    environment
			    history
			    select-cadr))))

;;;; Definitions

(define-er-macro-transformer 'DEFINE system-global-environment
  (let ((keyword
	 (classifier->keyword
	  (lambda (form environment definition-environment history)
	    (classify/define form environment definition-environment history
			     variable-binding-theory)))))
    (lambda (form rename compare)
      compare				;ignore
      (cond ((syntax-match? '((IDENTIFIER . MIT-BVL) + FORM) (cdr form))
	     `(,(car form) ,(caadr form)
			   (,(rename 'NAMED-LAMBDA) ,@(cdr form))))
	    ((syntax-match? '((DATUM . MIT-BVL) + FORM) (cdr form))
	     `(,(car form) ,(caadr form)
			   (,(rename 'LAMBDA) ,(cdadr form) ,@(cddr form))))
	    ((syntax-match? '(IDENTIFIER) (cdr form))
	     `(,keyword ,(cadr form) ,(unassigned-expression)))
	    ((syntax-match? '(IDENTIFIER EXPRESSION) (cdr form))
	     `(,keyword ,(cadr form) ,(caddr form)))
	    (else
	     (ill-formed-syntax form))))))

(define-classifier 'DEFINE-SYNTAX system-global-environment
  (lambda (form environment definition-environment history)
    (syntax-check '(KEYWORD IDENTIFIER EXPRESSION) form history)
    (classify/define form environment definition-environment history
		     syntactic-binding-theory)))

(define (classify/define form environment definition-environment history
			 binding-theory)
  (if (not (syntactic-environment/top-level? definition-environment))
      (syntactic-environment/define definition-environment
				    (cadr form)
				    (make-reserved-name-item history)))
  (binding-theory definition-environment
		  (cadr form)
		  (classify/subexpression (caddr form)
					  environment
					  history
					  select-caddr)
		  history))

(define (syntactic-binding-theory environment name item history)
  (if (not (keyword-item? item))
      (let ((history (item/history item)))
	(syntax-error history "Syntactic binding value must be a keyword:"
		      (history/original-form history))))
  (overloaded-binding-theory environment name item history))

(define (variable-binding-theory environment name item history)
  (if (keyword-item? item)
      (let ((history (item/history item)))
	(syntax-error history "Binding value may not be a keyword:"
		      (history/original-form history))))
  (overloaded-binding-theory environment name item history))

(define (overloaded-binding-theory environment name item history)
  (if (keyword-item? item)
      (begin
	(syntactic-environment/define environment
				      name
				      (item/new-history item #f))
	;; User-defined macros at top level are preserved in the output.
	(if (and (keyword-value-item? item)
		 (syntactic-environment/top-level? environment))
	    (make-binding-item history name item)
	    (make-null-binding-item history)))
      (make-binding-item history (bind-variable! environment name) item)))

;;;; SRFI features

(define-er-macro-transformer 'COND-EXPAND system-global-environment
  (lambda (form rename compare)
    (let ((if-error (lambda () (ill-formed-syntax form))))
      (if (syntax-match? '(+ (DATUM * FORM)) (cdr form))
	  (let loop ((clauses (cdr form)))
	    (let ((req (caar clauses))
		  (if-true (lambda () `(,(rename 'BEGIN) ,@(cdar clauses)))))
	      (if (and (identifier? req)
		       (compare (rename 'ELSE) req))
		  (if (null? (cdr clauses))
		      (if-true)
		      (if-error))
		  (let req-loop
		      ((req req)
		       (if-true if-true)
		       (if-false
			(lambda ()
			  (if (null? (cdr clauses))
			      (if-error)
			      (loop (cdr clauses))))))
		    (cond ((identifier? req)
			   (if (there-exists? supported-srfi-features
				 (lambda (feature)
				   (compare (rename feature) req)))
			       (if-true)
			       (if-false)))
			  ((and (syntax-match? '(IDENTIFIER DATUM) req)
				(compare (rename 'NOT) (car req)))
			   (req-loop (cadr req)
				     if-false
				     if-true))
			  ((and (syntax-match? '(IDENTIFIER * DATUM) req)
				(compare (rename 'AND) (car req)))
			   (let and-loop ((reqs (cdr req)))
			     (if (pair? reqs)
				 (req-loop (car reqs)
					   (lambda () (and-loop (cdr reqs)))
					   if-false)
				 (if-true))))
			  ((and (syntax-match? '(IDENTIFIER * DATUM) req)
				(compare (rename 'OR) (car req)))
			   (let or-loop ((reqs (cdr req)))
			     (if (pair? reqs)
				 (req-loop (car reqs)
					   if-true
					   (lambda () (or-loop (cdr reqs))))
				 (if-false))))
			  (else
			   (if-error)))))))
	  (if-error)))))

(define supported-srfi-features
  '(SRFI-0
    SRFI-6
    SRFI-8
    SRFI-9
    SRFI-23
    SRFI-30))

(define-er-macro-transformer 'RECEIVE system-global-environment
  (lambda (form rename compare)
    compare				;ignore
    (if (syntax-match? '(R4RS-BVL FORM + FORM) (cdr form))
	`(,(rename 'CALL-WITH-VALUES)
	  (,(rename 'LAMBDA) () ,(caddr form))
	  (,(rename 'LAMBDA) ,(cadr form) ,@(cdddr form)))
	(ill-formed-syntax form))))

(define-er-macro-transformer 'DEFINE-RECORD-TYPE system-global-environment
  (lambda (form rename compare)
    compare				;ignore
    (if (syntax-match? '(IDENTIFIER
			 (IDENTIFIER * IDENTIFIER)
			 IDENTIFIER
			 * (IDENTIFIER IDENTIFIER ? IDENTIFIER))
		       (cdr form))
	(let ((type (cadr form))
	      (constructor (car (caddr form)))
	      (c-tags (cdr (caddr form)))
	      (predicate (cadddr form))
	      (fields (cddddr form))
	      (de (rename 'DEFINE)))
	  `(,(rename 'BEGIN)
	    (,de ,type (,(rename 'MAKE-RECORD-TYPE) ',type ',(map car fields)))
	    (,de ,constructor (,(rename 'RECORD-CONSTRUCTOR) ,type ',c-tags))
	    (,de ,predicate (,(rename 'RECORD-PREDICATE) ,type))
	    ,@(append-map
	       (lambda (field)
		 (let ((name (car field)))
		   (cons `(,de ,(cadr field)
			       (,(rename 'RECORD-ACCESSOR) ,type ',name))
			 (if (pair? (cddr field))
			     `((,de ,(caddr field)
				    (,(rename 'RECORD-MODIFIER) ,type ',name)))
			     '()))))
	       fields)))
	(ill-formed-syntax form))))

;;;; LET-like

(define-er-macro-transformer 'LET system-global-environment
  (let ((keyword
	 (classifier->keyword
	  (lambda (form environment definition-environment history)
	    definition-environment
	    (let* ((binding-environment
		    (make-internal-syntactic-environment environment))
		   (body-environment
		    (make-internal-syntactic-environment binding-environment)))
	      (classify/let-like form
				 environment
				 binding-environment
				 body-environment
				 history
				 variable-binding-theory
				 output/let))))))
    (lambda (form rename compare)
      compare				;ignore
      (cond ((syntax-match? '(IDENTIFIER (* (IDENTIFIER ? EXPRESSION)) + FORM)
			    (cdr form))
	     (let ((name (cadr form))
		   (bindings (caddr form))
		   (body (cdddr form)))
	       `((,(rename 'LETREC)
		  ((,name (,(rename 'LAMBDA) ,(map car bindings) ,@body)))
		  ,name)
		 ,@(map (lambda (binding)
			  (if (pair? (cdr binding))
			      (cadr binding)
			      (unassigned-expression)))
			bindings))))
	    ((syntax-match? '((* (IDENTIFIER ? EXPRESSION)) + FORM) (cdr form))
	     `(,keyword ,@(cdr (normalize-let-bindings form))))
	    (else
	     (ill-formed-syntax form))))))

(define-er-macro-transformer 'LET* system-global-environment
  (lambda (form rename compare)
    compare			;ignore
    (expand/let* form rename 'LET)))

(define-classifier 'LETREC system-global-environment
  (lambda (form environment definition-environment history)
    definition-environment
    (syntax-check '(KEYWORD (* (IDENTIFIER ? EXPRESSION)) + FORM) form history)
    (let* ((binding-environment
	    (make-internal-syntactic-environment environment))
	   (body-environment
	    (make-internal-syntactic-environment binding-environment)))
      (for-each (let ((item (make-reserved-name-item history)))
		  (lambda (binding)
		    (syntactic-environment/define binding-environment
						  (car binding)
						  item)))
		(cadr form))
      (classify/let-like form
			 binding-environment
			 binding-environment
			 body-environment
			 history
			 variable-binding-theory
			 output/letrec))))

(define (normalize-let-bindings form)
  `(,(car form) ,(map (lambda (binding)
			(if (pair? (cdr binding))
			    binding
			    (list (car binding) (unassigned-expression))))
		      (cadr form))
		,@(cddr form)))

(define-classifier 'LET-SYNTAX system-global-environment
  (lambda (form environment definition-environment history)
    definition-environment
    (syntax-check '(KEYWORD (* (IDENTIFIER EXPRESSION)) + FORM) form history)
    (let* ((binding-environment
	    (make-internal-syntactic-environment environment))
	   (body-environment
	    (make-internal-syntactic-environment binding-environment)))
      (classify/let-like form
			 environment
			 binding-environment
			 body-environment
			 history
			 syntactic-binding-theory
			 output/let))))

(define-er-macro-transformer 'LET*-SYNTAX system-global-environment
  (lambda (form rename compare)
    compare			;ignore
    (expand/let* form rename 'LET-SYNTAX)))

(define-classifier 'LETREC-SYNTAX system-global-environment
  (lambda (form environment definition-environment history)
    definition-environment
    (syntax-check '(KEYWORD (* (IDENTIFIER EXPRESSION)) + FORM) form history)
    (let* ((binding-environment
	    (make-internal-syntactic-environment environment))
	   (body-environment
	    (make-internal-syntactic-environment binding-environment)))
      (for-each (let ((item (make-reserved-name-item history)))
		  (lambda (binding)
		    (syntactic-environment/define binding-environment
						  (car binding)
						  item)))
		(cadr form))
      (classify/let-like form
			 binding-environment
			 binding-environment
			 body-environment
			 history
			 syntactic-binding-theory
			 output/letrec))))

(define (classify/let-like form
			   value-environment
			   binding-environment
			   body-environment
			   history
			   binding-theory
			   output/let)
  ;; Classify right-hand sides first, in order to catch references to
  ;; reserved names.  Then bind names prior to classifying body.
  (let* ((bindings
	  (delete-matching-items!
	      (map (lambda (binding item)
		     (binding-theory binding-environment
				     (car binding)
				     item
				     history))
		   (cadr form)
		   (select-map (lambda (binding selector)
				 (classify/subexpression (cadr binding)
							 value-environment
							 history
							 (selector/add-cadr
							  selector)))
			       (cadr form)
			       select-cadr))
	    null-binding-item?))
	 (body
	  (classify/body (cddr form)
			 body-environment
			 body-environment
			 history
			 select-cddr)))
    (if (eq? binding-theory syntactic-binding-theory)
	body
	(make-expression-item history
	 (lambda ()
	   (output/let (map binding-item/name bindings)
		       (map (lambda (binding)
			      (compile-item/expression
			       (binding-item/value binding)))
			    bindings)
		       (compile-body-item body)))))))

(define (expand/let* form rename let-keyword)
  (capture-expansion-history
   (lambda (history)
     (syntax-check '(KEYWORD (* DATUM) + FORM) form history)
     (let ((bindings (cadr form))
	   (body (cddr form))
	   (keyword (rename let-keyword)))
       (if (pair? bindings)
	   (let loop ((bindings bindings))
	     (if (pair? (cdr bindings))
		 `(,keyword (,(car bindings)) ,(loop (cdr bindings)))
		 `(,keyword ,bindings ,@body)))
	   `(,keyword ,bindings ,@body))))))

;;;; Bodies

(define (compile-body-item item)
  (call-with-values
      (lambda ()
	(extract-declarations-from-body (body-item/components item)))
    (lambda (declaration-items items)
      (output/body (map declaration-item/text declaration-items)
		   (compile-body-items item items)))))

;;;; Derived syntax

(define-er-macro-transformer 'AND system-global-environment
  (lambda (form rename compare)
    compare				;ignore
    (capture-expansion-history
     (lambda (history)
       (syntax-check '(KEYWORD * EXPRESSION) form history)
       (let ((operands (cdr form)))
	 (if (pair? operands)
	     (let ((if-keyword (rename 'IF)))
	       (let loop ((operands operands))
		 (if (pair? (cdr operands))
		     `(,if-keyword ,(car operands)
				   ,(loop (cdr operands))
				   #F)
		     (car operands))))
	     `#T))))))

(define-compiler 'OR system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD * EXPRESSION) form history)
    (if (pair? (cdr form))
	(let loop ((expressions (cdr form)) (selector select-cdr))
	  (let ((compiled
		 (compile/subexpression (car expressions)
					environment
					history
					(selector/add-car selector))))
	    (if (pair? (cdr expressions))
		(output/disjunction compiled
				    (loop (cdr expressions)
					  (selector/add-cdr selector)))
		compiled)))
	`#F)))

(define-er-macro-transformer 'CASE system-global-environment
  (lambda (form rename compare)
    (capture-expansion-history
     (lambda (history)
       (syntax-check '(KEYWORD EXPRESSION + (DATUM + EXPRESSION)) form history)
       (call-with-syntax-error-procedure
	(lambda (syntax-error)
	  (letrec
	      ((process-clause
		(lambda (clause rest)
		  (cond ((null? (car clause))
			 (process-rest rest))
			((and (identifier? (car clause))
			      (compare (rename 'ELSE) (car clause))
			      (null? rest))
			 `(,(rename 'BEGIN) ,@(cdr clause)))
			((list? (car clause))
			 `(,(rename 'IF) ,(process-predicate (car clause))
					 (,(rename 'BEGIN) ,@(cdr clause))
					 ,(process-rest rest)))
			(else
			 (syntax-error "Ill-formed clause:" clause)))))
	       (process-rest
		(lambda (rest)
		  (if (pair? rest)
		      (process-clause (car rest) (cdr rest))
		      (unspecific-expression))))
	       (process-predicate
		(lambda (items)
		  ;; Optimize predicate for speed in compiled code.
		  (cond ((null? (cdr items))
			 (single-test (car items)))
			((null? (cddr items))
			 `(,(rename 'OR) ,(single-test (car items))
					 ,(single-test (cadr items))))
			((null? (cdddr items))
			 `(,(rename 'OR) ,(single-test (car items))
					 ,(single-test (cadr items))
					 ,(single-test (caddr items))))
			((null? (cddddr items))
			 `(,(rename 'OR) ,(single-test (car items))
					 ,(single-test (cadr items))
					 ,(single-test (caddr items))
					 ,(single-test (cadddr items))))
			(else
			 `(,(rename
			     (if (for-all? items eq-testable?) 'MEMQ 'MEMV))
			   ,(rename 'TEMP)
			   ',items)))))
	       (single-test
		(lambda (item)
		  `(,(rename (if (eq-testable? item) 'EQ? 'EQV?))
		    ,(rename 'TEMP)
		    ',item)))
	       (eq-testable?
		(lambda (item)
		  (or (symbol? item)
		      (boolean? item)
		      ;; remainder are implementation dependent:
		      (char? item)	
		      (fix:fixnum? item)))))
	    `(,(rename 'LET) ((,(rename 'TEMP) ,(cadr form)))
			     ,(process-clause (caddr form)
					      (cdddr form))))))))))

(define-er-macro-transformer 'COND system-global-environment
  (lambda (form rename compare)
    (capture-expansion-history
     (lambda (history)
       (let ((clauses (cdr form)))
	 (if (not (pair? clauses))
	     (syntax-error history "Form must have at least one clause:" form))
	 (let loop ((clause (car clauses)) (rest (cdr clauses)))
	   (expand/cond-clause clause rename compare history (null? rest)
			       (if (pair? rest)
				   (loop (car rest) (cdr rest))
				   (unspecific-expression)))))))))

(define-er-macro-transformer 'DO system-global-environment
  (lambda (form rename compare)
    (capture-expansion-history
     (lambda (history)
       (syntax-check '(KEYWORD (* (IDENTIFIER EXPRESSION ? EXPRESSION))
			       (+ FORM)
			       * FORM)
		      form history)
       (let ((bindings (cadr form))
	     (r-loop (rename 'DO-LOOP)))
	 `(,(rename 'LET)
	   ,r-loop
	   ,(map (lambda (binding)
		   (list (car binding) (cadr binding)))
		 bindings)
	   ,(expand/cond-clause (caddr form) rename compare history #f
				`(,(rename 'BEGIN)
				  ,@(cdddr form)
				  (,r-loop ,@(map (lambda (binding)
						    (if (pair? (cddr binding))
							(caddr binding)
							(car binding)))
						  bindings))))))))))

(define (expand/cond-clause clause rename compare history else-allowed?
			    alternative)
  (if (not (and (pair? clause) (list? (cdr clause))))
      (syntax-error history "Ill-formed clause:" clause))
  (cond ((and (identifier? (car clause))
	      (compare (rename 'ELSE) (car clause)))
	 (if (not else-allowed?)
	     (syntax-error history "Misplaced ELSE clause:" clause))
	 (if (or (not (pair? (cdr clause)))
		 (and (identifier? (cadr clause))
		      (compare (rename '=>) (cadr clause))))
	     (syntax-error history "Ill-formed ELSE clause:" clause))
	 `(,(rename 'BEGIN) ,@(cdr clause)))
	((not (pair? (cdr clause)))
	 (let ((r-temp (rename 'TEMP)))
	   `(,(rename 'LET) ((,r-temp ,(car clause)))
			    (,(rename 'IF) ,r-temp ,r-temp ,alternative))))
	((and (identifier? (cadr clause))
	      (compare (rename '=>) (cadr clause)))
	 (if (not (and (pair? (cddr clause))
		       (null? (cdddr clause))))
	     (syntax-error history "Ill-formed => clause:" clause))
	 (let ((r-temp (rename 'TEMP)))
	   `(,(rename 'LET) ((,r-temp ,(car clause)))
			    (,(rename 'IF) ,r-temp
					   (,(caddr clause) ,r-temp)
					   ,alternative))))
	(else
	 `(,(rename 'IF) ,(car clause)
			 (,(rename 'BEGIN) ,@(cdr clause))
			 ,alternative))))

(define-er-macro-transformer 'QUASIQUOTE system-global-environment
  (lambda (form rename compare)
    (call-with-syntax-error-procedure
     (lambda (syntax-error)
       (define (descend-quasiquote x level return)
	 (cond ((pair? x) (descend-quasiquote-pair x level return))
	       ((vector? x) (descend-quasiquote-vector x level return))
	       (else (return 'QUOTE x))))
       (define (descend-quasiquote-pair x level return)
	 (cond ((not (and (pair? x)
			  (identifier? (car x))
			  (pair? (cdr x))
			  (null? (cddr x))))
		(descend-quasiquote-pair* x level return))
	       ((compare (rename 'QUASIQUOTE) (car x))
		(descend-quasiquote-pair* x (+ level 1) return))
	       ((compare (rename 'UNQUOTE) (car x))
		(if (zero? level)
		    (return 'UNQUOTE (cadr x))
		    (descend-quasiquote-pair* x (- level 1) return)))
	       ((compare (rename 'UNQUOTE-SPLICING) (car x))
		(if (zero? level)
		    (return 'UNQUOTE-SPLICING (cadr x))
		    (descend-quasiquote-pair* x (- level 1) return)))
	       (else
		(descend-quasiquote-pair* x level return))))
       (define (descend-quasiquote-pair* x level return)
	 (descend-quasiquote (car x) level
	   (lambda (car-mode car-arg)
	     (descend-quasiquote (cdr x) level
	       (lambda (cdr-mode cdr-arg)
		 (cond ((and (eq? car-mode 'QUOTE) (eq? cdr-mode 'QUOTE))
			(return 'QUOTE x))
		       ((eq? car-mode 'UNQUOTE-SPLICING)
			(if (and (eq? cdr-mode 'QUOTE) (null? cdr-arg))
			    (return 'UNQUOTE car-arg)
			    (return 'APPEND
				    (list car-arg
					  (finalize-quasiquote cdr-mode
							       cdr-arg)))))
		       ((and (eq? cdr-mode 'QUOTE) (list? cdr-arg))
			(return 'LIST
				(cons (finalize-quasiquote car-mode car-arg)
				      (map (lambda (element)
					     (finalize-quasiquote 'QUOTE
								  element))
					   cdr-arg))))
		       ((eq? cdr-mode 'LIST)
			(return 'LIST
				(cons (finalize-quasiquote car-mode car-arg)
				      cdr-arg)))
		       (else
			(return
			 'CONS
			 (list (finalize-quasiquote car-mode car-arg)
			       (finalize-quasiquote cdr-mode cdr-arg))))))))))
       (define (descend-quasiquote-vector x level return)
	 (descend-quasiquote (vector->list x) level
	   (lambda (mode arg)
	     (case mode
	       ((QUOTE) (return 'QUOTE x))
	       ((LIST) (return 'VECTOR arg))
	       (else
		(return 'LIST->VECTOR
			(list (finalize-quasiquote mode arg))))))))
       (define (finalize-quasiquote mode arg)
	 (case mode
	   ((QUOTE) `(,(rename 'QUOTE) ,arg))
	   ((UNQUOTE) arg)
	   ((UNQUOTE-SPLICING) (syntax-error ",@ in illegal context:" arg))
	   (else `(,(rename mode) ,@arg))))
       (capture-expansion-history
	(lambda (history)
	  (syntax-check '(KEYWORD EXPRESSION) form history)
	  (descend-quasiquote (cadr form) 0 finalize-quasiquote)))))))

;;;; MIT-specific syntax

(define-er-macro-transformer 'ACCESS system-global-environment
  (let ((keyword
	 (classifier->keyword
	  (lambda (form environment definition-environment history)
	    definition-environment
	    (make-access-item history
			      (cadr form)
			      (classify/subexpression (caddr form)
						      environment
						      history
						      select-caddr))))))
    (lambda (form rename compare)
      rename compare			;ignore
      (cond ((syntax-match? '(IDENTIFIER EXPRESSION) (cdr form))
	     `(,keyword ,@(cdr form)))
	    ((syntax-match? '(IDENTIFIER IDENTIFIER + FORM) (cdr form))
	     `(,keyword ,(cadr form) (,(car form) ,@(cddr form))))
	    (else
	     (ill-formed-syntax form))))))

(define <access-item>
  (make-item-type "access-item" '(NAME ENVIRONMENT)
    (lambda (item)
      (output/access-reference
       (access-item/name item)
       (compile-item/expression (access-item/environment item))))))

(define make-access-item
  (item-constructor <access-item> '(NAME ENVIRONMENT)))

(define access-item?
  (item-predicate <access-item>))

(define access-item/name
  (item-accessor <access-item> 'NAME))

(define access-item/environment
  (item-accessor <access-item> 'ENVIRONMENT))

(define-er-macro-transformer 'CONS-STREAM system-global-environment
  (lambda (form rename compare)
    compare				;ignore
    (capture-expansion-history
     (lambda (history)
       (syntax-check '(KEYWORD EXPRESSION EXPRESSION) form history)
       `(,(rename 'CONS) ,(cadr form)
			 (,(rename 'DELAY) ,(caddr form)))))))

(define-compiler 'DEFAULT-OBJECT? system-global-environment
  (lambda (form environment history)
    (syntax-check '(KEYWORD IDENTIFIER) form history)
    (let ((item
	   (classify/subexpression (cadr form)
				   environment
				   history
				   select-cadr)))
      (if (not (variable-item? item))
	  (syntax-error history "Variable required in this context:" form))
      (output/unassigned-test (variable-item/name item)))))

(define-er-macro-transformer 'DEFINE-INTEGRABLE system-global-environment
  (lambda (form rename compare)
    compare				;ignore
    (let ((r-declare (rename 'DECLARE)))
      (cond ((syntax-match? '(IDENTIFIER EXPRESSION) (cdr form))
	     `(,(rename 'BEGIN)
	       (,r-declare (INTEGRATE ,(cadr form)))
	       (,(rename 'DEFINE) ,@(cdr form))))
	    ((syntax-match? '((IDENTIFIER * IDENTIFIER) + FORM) (cdr form))
	     `(,(rename 'BEGIN)
	       (,r-declare (INTEGRATE-OPERATOR ,(caadr form)))
	       (,(rename 'DEFINE) ,(cadr form)
				  (,r-declare (INTEGRATE ,@(cdadr form)))
				  ,@(cddr form))))
	    (else
	     (ill-formed-syntax form))))))

(define-er-macro-transformer 'FLUID-LET system-global-environment
  (lambda (form rename compare)
    compare
    (capture-expansion-history
     (lambda (history)
       (syntax-check '(KEYWORD (* (FORM ? EXPRESSION)) + FORM)
		     form history)
       (let ((names (map car (cadr form)))
	     (r-let (rename 'LET))
	     (r-lambda (rename 'LAMBDA))
	     (r-set! (rename 'SET!)))
	 (let ((out-temps
		(map (lambda (name)
		       name
		       (make-synthetic-identifier 'OUT-TEMP))
		     names))
	       (in-temps
		(map (lambda (name)
		       name
		       (make-synthetic-identifier 'IN-TEMP))
		     names))
	       (swap
		(lambda (tos names froms)
		  `(,r-lambda ()
			      ,@(map (lambda (to name from)
				       `(,r-set! ,to
						 (,r-set! ,name
							  (,r-set! ,from))))
				     tos
				     names
				     froms)
			      ,(unspecific-expression)))))
	   `(,r-let (,@(map cons in-temps (map cdr (cadr form)))
		     ,@(map list out-temps))
		    (,(rename 'SHALLOW-FLUID-BIND)
		     ,(swap out-temps names in-temps)
		     (,r-lambda () ,@(cddr form))
		     ,(swap in-temps names out-temps)))))))))

(define-compiler 'THE-ENVIRONMENT system-global-environment
  (lambda (form environment history)
    environment
    (syntax-check '(KEYWORD) form history)
    (if (not (syntactic-environment/top-level? environment))
	(syntax-error history "This form allowed only at top level:" form))
    (output/the-environment)))

(define (unspecific-expression)
  (compiler->form
   (lambda (form environment history)
     form environment history		;ignore
     (output/unspecific))))

(define (unassigned-expression)
  (compiler->form
   (lambda (form environment history)
     form environment history		;ignore
     (output/unassigned))))

;;;; Declarations

(define-classifier 'DECLARE system-global-environment
  (lambda (form environment definition-environment history)
    definition-environment
    (syntax-check '(KEYWORD * (SYMBOL * DATUM)) form history)
    (make-declaration-item history
			   (lambda ()
			     (map-declaration-references (cdr form)
							 environment
							 history
							 select-cdr)))))

(define-classifier 'LOCAL-DECLARE system-global-environment
  (lambda (form environment definition-environment history)
    (syntax-check '(KEYWORD (* (SYMBOL * DATUM)) + FORM) form history)
    (let ((body
	   (classify/body (cddr form)
			  environment
			  definition-environment
			  history
			  select-cddr)))
      (make-expression-item history
	(lambda ()
	  (output/local-declare (map-declaration-references (cadr form)
							    environment
							    history
							    select-cadr)
				(compile-body-item body)))))))

(define (map-declaration-references declarations environment history selector)
  (select-map (lambda (declaration selector)
		(process-declaration declaration selector
		  (lambda (form selector)
		    (classify/variable-subexpression form
						     environment
						     history
						     selector))
		  (lambda (declaration selector)
		    (syntax-error (history/add-subproblem declaration
							  environment
							  history
							  selector)
				  "Ill-formed declaration:"
				  declaration))))
	      declarations
	      selector))

(define (classify/variable-subexpression form environment history selector)
  (let ((item (classify/subexpression form environment history selector)))
    (if (not (variable-item? item))
	(syntax-error history "Variable required in this context:" form))
    (variable-item/name item)))