#| -*-Scheme-*-

$Id: syntax.scm,v 1.31 2003/02/14 18:28:01 cph Exp $

Copyright (c) 1988-1999, 2001, 2002 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.

|#

;;;; LAP Syntaxer
;;; package: (compiler lap-syntaxer)

(declare (usual-integrations))

(define-integrable cons-syntax cons)
(define-integrable append-syntax! append!)

#|
(define (cons-syntax directive directives)
  (if (and (bit-string? directive)
	   (not (null? directives))
	   (bit-string? (car directives)))
      (begin (set-car! directives
		       (instruction-append directive (car directives)))
	     directives)
      (cons directive directives)))

(define (append-syntax! directives1 directives2)
  (cond ((null? directives1) directives2)
	((null? directives2) directives1)
	(else
	 (let ((tail (last-pair directives1)))
	   (if (and (bit-string? (car tail))
		    (bit-string? (car directives2)))
	       (begin
		 (set-car! tail
			   (instruction-append (car tail) (car directives2)))
		 (set-cdr! tail (cdr directives2)))
	       (set-cdr! tail directives2))
	   directives1))))
|#

(define (lap:syntax-instruction instruction)
  (if (memq (car instruction)
	    '(EQUATE SCHEME-OBJECT SCHEME-EVALUATION
		     ENTRY-POINT LABEL BLOCK-OFFSET
		     PADDING))
      (list instruction)
      (let ((match-result (instruction-lookup instruction)))
	(if (not match-result)
	    (error "illegal instruction syntax" instruction))
	(match-result))))

(define (instruction-lookup instruction)
  (pattern-lookup
   (cdr (or (assq (car instruction) instructions)
	    (error "INSTRUCTION-LOOKUP: Unknown keyword" (car instruction))))
   (cdr instruction)))

(define (add-instruction! keyword lookup)
  (let ((entry (assq keyword instructions)))
    (if entry
	(set-cdr! entry lookup)
	(set! instructions (cons (cons keyword lookup) instructions))))
  keyword)

(define instructions
  '())

(define (integer-syntaxer expression environment coercion-type size)
  (let ((name (make-coercion-name coercion-type size)))
    (if (exact-integer? expression)
	`',((lookup-coercion name) expression)
	`(,(close-syntax 'SYNTAX-EVALUATION environment) ,expression ,name))))

(define (syntax-evaluation expression coercion)
  (if (exact-integer? expression)
      (coercion expression)
      `(EVALUATION ,expression ,(coercion-size coercion) ,coercion)))

(define (optimize-group . components)
  (optimize-group-internal components
    (lambda (result make-group?)
      (if make-group?
	  `(GROUP ,@result)
	  result))))

(define-integrable optimize-group-early
  optimize-group)

(define optimize-group-internal
  (let ()
    (define (loop1 components)
      (cond ((null? components) '())
	    ((bit-string? (car components))
	     (loop2 (car components) (cdr components)))
	    (else
	     (cons (car components)
		   (loop1 (cdr components))))))

    (define (loop2 bit-string components)
      (cond ((null? components)
	     (list bit-string))
	    ((bit-string? (car components))
	     (loop2 (instruction-append bit-string (car components))
		    (cdr components)))
	    (else
	     (cons bit-string
		   (cons (car components)
			 (loop1 (cdr components)))))))

    (lambda (components receiver)
      (let ((components (loop1 components)))
	(if (null? components)
	    (error "OPTIMIZE-GROUP: No components"))
	(if (null? (cdr components))
	    (receiver (car components) false)
	    (receiver components true))))))

;;;; Variable width expression processing

(define (variable-width-expression-syntaxer name expression environment
					    clauses)
  (if (exact-integer? expression)
      (let ((chosen (choose-clause expression clauses)))
	`(,(close-syntax 'LET environment)
	  ((,name ,expression))
	  (,(close-syntax 'DECLARE environment) (INTEGRATE ,name))
	  ,name				;ignore if not referenced
	  (,(close-syntax 'CAR environment) ,(car chosen))))
      `(,(close-syntax 'SYNTAX-VARIABLE-WIDTH-EXPRESSION environment)
	,expression
	(,(close-syntax 'LIST environment)
	 ,@(map (lambda (clause)
		  `(,(close-syntax 'CONS environment)
		    (,(close-syntax 'LAMBDA environment)
		     (,name)
		     ,name		;ignore if not referenced
		     ,(car clause))
		    ',(cdr clause)))
		clauses)))))

(define (syntax-variable-width-expression expression clauses)
  (if (exact-integer? expression)
      (let ((chosen (choose-clause expression clauses)))
	(car ((car chosen) expression)))
      `(VARIABLE-WIDTH-EXPRESSION
	,expression
	,@clauses)))

(define (choose-clause value clauses)
  (if (not (pair? clauses))
      (error "Value out of range:" value))
  (if (let ((low (caddr (car clauses)))
	    (high (cadddr (car clauses))))
	(and (or (null? low)
		 (<= low value))
	     (or (null? high)
		 (<= value high))))
      (car clauses)
      (choose-clause value (cdr clauses))))

;;;; Coercion Machinery

(define (make-coercion-name coercion-type size)
  (intern
   (string-append "coerce-"
		  (number->string size)
		  "-bit-"
		  (symbol->string coercion-type))))

(define coercion-property-tag
  "Coercion")

(define ((coercion-maker coercion-types) coercion-type size)
  (let ((coercion
	 ((cdr (or (assq coercion-type coercion-types)
		   (error "Unknown coercion type" coercion-type)))
	  size)))
    (2D-put! coercion coercion-property-tag (list coercion-type size))
    coercion))

(define (coercion-size coercion)
  (cadr (coercion-properties coercion)))

(define (unmake-coercion coercion receiver)
  (apply receiver (coercion-properties coercion)))

(define (coercion-properties coercion)
  (or (2D-get coercion coercion-property-tag)
      (error "COERCION-PROPERTIES: Not a known coercion" coercion)))

(define coercion-environment
  (->environment '(COMPILER LAP-SYNTAXER)))

(define-integrable (lookup-coercion name)
  (lexical-reference coercion-environment name))

(define ((coerce-unsigned-integer nbits) n)
  (unsigned-integer->bit-string nbits n))

(define (coerce-signed-integer nbits)
  (let* ((limit (expt 2 (-1+ nbits)))
	 (offset (+ limit limit)))
    (lambda (n)
      (unsigned-integer->bit-string
       nbits
       (cond ((negative? n) (+ n offset))
	     ((< n limit) n)
	     (else (error "Integer too large to be encoded" n)))))))

(define (standard-coercion kernel)
  (lambda (nbits)
    (lambda (n)
      (unsigned-integer->bit-string nbits (kernel n)))))