#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019, 2020 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Parser language

;;; A parser is a procedure of one argument, a parser buffer.  It
;;; attempts to parse the contents of the buffer, starting at the
;;; location of the buffer pointer.  If the parse is successful, the
;;; buffer pointer is advanced to the end of the parsed segment, and a
;;; vector of results is returned.  If the parse fails, the buffer
;;; pointer is unchanged, and #F is returned.

(declare (usual-integrations))

;;;; Preprocessor

(define (preprocess-parser-expression expression
				      external-bindings
				      internal-bindings)
  (cond ((and (pair? expression)
	      (symbol? (car expression))
	      (list? (cdr expression)))
	 (let ((preprocessor (parser-preprocessor (car expression))))
	   (if preprocessor
	       (preprocessor expression external-bindings internal-bindings)
	       (error "Unknown parser expression:" expression))))
	((symbol? expression)
	 (let ((preprocessor (parser-preprocessor expression)))
	   (if preprocessor
	       (preprocessor expression external-bindings internal-bindings)
	       expression)))
	((identifier? expression)
	 expression)
	((or (string? expression)
	     (char? expression))
	 (preprocess-parser-expression `(NOISE ,expression)
				       external-bindings
				       internal-bindings))
	(else
	 (error "Unknown parser expression:" expression))))

(define (preprocess-parser-expressions expressions
				       external-bindings
				       internal-bindings)
  (map (lambda (expression)
	 (preprocess-parser-expression expression
				       external-bindings
				       internal-bindings))
       expressions))

(define (define-parser-preprocessor name procedure)
  (if (pair? name)
      (for-each (lambda (name) (define-parser-preprocessor name procedure))
		name)
      (hash-table-set! parser-preprocessors name procedure))
  name)

(define-syntax define-*parser-macro
  (rsc-macro-transformer
   (lambda (form environment)
     (let ((r-dpe (close-syntax 'DEFINE-*PARSER-EXPANDER environment))
	   (r-lambda (close-syntax 'LAMBDA environment)))
       (cond ((syntax-match? '(symbol expression) (cdr form))
	      `(,r-dpe ',(cadr form)
		       (,r-lambda ()
				  ,(caddr form))))
	     ((syntax-match? '((symbol . mit-bvl) + expression) (cdr form))
	      `(,r-dpe ',(car (cadr form))
		       (,r-lambda ,(cdr (cadr form))
				  ,@(cddr form))))
	     (else
	      (ill-formed-syntax form)))))))

(define (define-*parser-expander name procedure)
  (define-parser-macro name
    (lambda (expression external-bindings internal-bindings)
      (preprocess-parser-expression (if (pair? expression)
					(apply procedure (cdr expression))
					(procedure))
				    external-bindings
				    internal-bindings))))

(define (parser-preprocessor name)
  (or (lookup-parser-macro name)
      (hash-table-ref/default parser-preprocessors name #f)))

(define parser-preprocessors
  (make-strong-eq-hash-table))

(define-*parser-expander '+
  (lambda (expression)
    `(SEQ ,expression (* ,expression))))

(define-*parser-expander '?
  (lambda (expression)
    `(ALT ,expression (SEQ))))

(define-*parser-expander 'COMPLETE
  (lambda (expression)
    `(SEQ ,expression (NOISE (END-OF-INPUT)))))

(define-*parser-expander 'TOP-LEVEL
  (lambda (expression)
    `(SEQ ,expression (DISCARD-MATCHED))))

(define-*parser-expander 'ERROR
  (lambda (ptr msg . irritants)
    (let ((v (generate-uninterned-symbol)))
      `(SEXP (LAMBDA (,v)
	       ,@(if ptr (list v) '())
	       (PARSER-BUFFER-ERROR ,(or ptr v) ,msg ,@irritants))))))

(define-*parser-expander 'ENCAPSULATE*
  (lambda (procedure expression)
    `(ENCAPSULATE (LAMBDA (V) (APPLY ,procedure (VECTOR->LIST V)))
		  ,expression)))

(define-*parser-expander 'TRANSFORM*
  (lambda (procedure expression)
    `(TRANSFORM (LAMBDA (V)
		  (CALL-WITH-VALUES
		      (LAMBDA ()
			(APPLY ,procedure (VECTOR->LIST V)))
		    VECTOR))
		,expression)))

(define-parser-preprocessor '(ALT SEQ)
  (lambda (expression external-bindings internal-bindings)
    `(,(car expression)
      ,@(flatten-expressions (preprocess-parser-expressions (cdr expression)
							    external-bindings
							    internal-bindings)
			     (car expression)))))

(define-parser-preprocessor '*
  (lambda (expression external-bindings internal-bindings)
    `(,(car expression)
      ,(preprocess-parser-expression (check-1-arg expression)
				     external-bindings
				     internal-bindings))))

(define-parser-preprocessor '(MATCH NOISE)
  (lambda (expression external-bindings internal-bindings)
    `(,(car expression)
      ,(preprocess-matcher-expression (check-1-arg expression)
				      external-bindings
				      internal-bindings))))

(define-parser-preprocessor '(TRANSFORM MAP ENCAPSULATE)
  (lambda (expression external-bindings internal-bindings)
    (check-2-args expression)
    `(,(car expression) ,(cadr expression)
			,(preprocess-parser-expression (caddr expression)
						       external-bindings
						       internal-bindings))))

(define-parser-preprocessor 'WITH-POINTER
  (lambda (expression external-bindings internal-bindings)
    (check-2-args expression (lambda (expression) (symbol? (cadr expression))))
    `(,(car expression) ,(cadr expression)
			,(preprocess-parser-expression (caddr expression)
						       external-bindings
						       internal-bindings))))

(define-parser-preprocessor 'SEXP
  (lambda (expression external-bindings internal-bindings)
    external-bindings internal-bindings
    (check-1-arg expression)
    expression))

(define-parser-preprocessor 'DISCARD-MATCHED
  (lambda (expression external-bindings internal-bindings)
    external-bindings internal-bindings
    (check-0-args expression)
    expression))

(define-parser-preprocessor 'VALUES
  (lambda (expression external-bindings internal-bindings)
    external-bindings internal-bindings
    expression))

;;;; Compiler

(define-syntax *parser
  (sc-macro-transformer
   (lambda (form environment)
     (if (syntax-match? '(expression) (cdr form))
	 (generate-parser-code (cadr form) environment)
	 (ill-formed-syntax form)))))

(define (generate-parser-code expression environment)
  (generate-external-procedure expression environment
			       preprocess-parser-expression
    (lambda (expression free-names)
      (call-with-pointer #f
	(lambda (p)
	  (bind-delayed-lambdas
	   (lambda (ks kf)
	     (compile-parser-expression expression #f ks kf free-names))
	   (make-parser-ks-lambda (lambda (v kf) kf v))
	   (backtracking-kf p (lambda () #f))))))))

(define (compile-parser-expression expression pointer ks kf free-names)
  (cond ((and (pair? expression)
	      (symbol? (car expression))
	      (list? (cdr expression))
	      (hash-table-ref/default parser-compilers (car expression) #f))
	 => (lambda (entry)
	      (let ((arity (car entry))
		    (compiler (cdr entry)))
		(if (and arity (not (= (length (cdr expression)) arity)))
		    (error "Incorrect arity for parser:" expression))
		(apply compiler pointer ks kf free-names (cdr expression)))))
	((or (symbol? expression)
	     (and (pair? expression) (eq? (car expression) 'SEXP)))
	 (wrap-external-parser `(,(protect (if (pair? expression)
					       (cadr expression)
					       expression)
					   free-names)
				 ,*buffer-name*)
			       ks
			       kf))
	(else
	 (error "Malformed parser:" expression))))

(define (wrap-external-parser expression ks kf)
  (with-value-binding expression
    (lambda (v)
      `(IF ,v
	   ,(delay-call ks v kf)
	   ,(delay-call kf)))))

(define-syntax define-parser
  (rsc-macro-transformer
   (lambda (form environment)
     (if (syntax-match? '((symbol . mit-bvl) + expression) (cdr form))
	 (let ((name (car (cadr form)))
	       (parameters (cdr (cadr form)))
	       (compiler-body (cddr form))
	       (r-dpc (close-syntax 'DEFINE-PARSER-COMPILER environment))
	       (r-lambda (close-syntax 'LAMBDA environment)))
	   `(,r-dpc ',name
		    ,(if (identifier? parameters) `#F (length parameters))
		    (,r-lambda (POINTER KS KF FREE-NAMES . ,parameters)
			       ,@compiler-body)))
	 (ill-formed-syntax form)))))

(define (define-parser-compiler keyword arity compiler)
  (hash-table-set! parser-compilers keyword (cons arity compiler))
  keyword)

(define parser-compilers
  (make-strong-eq-hash-table))

(define-parser (match expression)
  (call-with-pointer pointer
    (lambda (pointer)
      (bind-delayed-lambdas
       (lambda (ks)
	 (compile-matcher-expression expression pointer ks kf free-names))
       (make-matcher-ks-lambda
	(lambda (kf)
	  (delay-call ks
		      `(VECTOR
			(GET-PARSER-BUFFER-TAIL ,*buffer-name* ,pointer))
		      kf)))))))

(define-parser (noise expression)
  (bind-delayed-lambdas
   (lambda (ks)
     (compile-matcher-expression expression pointer ks kf free-names))
   (make-matcher-ks-lambda
     (lambda (kf)
       (delay-call ks `(VECTOR) kf)))))

(define-parser (values . expressions)
  pointer
  (delay-call ks
	      `(VECTOR ,@(map (lambda (expression)
				(protect expression free-names))
			      expressions))
	      kf))

(define-parser (transform transform expression)
  (post-processed-parser expression pointer ks kf free-names
    (lambda (ks v kf)
      (wrap-external-parser `(,(protect transform free-names) ,v) ks kf))))

(define-parser (map transform expression)
  (post-processed-parser expression pointer ks kf free-names
    (lambda (ks v kf)
      (delay-call ks `(VECTOR-MAP ,(protect transform free-names) ,v) kf))))

(define-parser (encapsulate transform expression)
  (post-processed-parser expression pointer ks kf free-names
    (lambda (ks v kf)
      (delay-call ks `(VECTOR (,(protect transform free-names) ,v)) kf))))

(define (post-processed-parser expression pointer ks kf free-names procedure)
  (bind-delayed-lambdas
   (lambda (ks)
     (compile-parser-expression expression pointer ks kf free-names))
   (make-parser-ks-lambda
    (lambda (v kf)
      (procedure ks v kf)))))

(define-parser (with-pointer identifier expression)
  `((LAMBDA (,identifier)
      ,(compile-parser-expression expression (or pointer identifier) ks kf
				  (cons identifier free-names)))
    ,(or pointer (fetch-pointer))))

(define-parser (discard-matched)
  pointer free-names
  `(BEGIN
     (DISCARD-PARSER-BUFFER-HEAD! ,*buffer-name*)
     ,(delay-call ks `(VECTOR) kf)))

(define-parser (seq . expressions)
  (if (pair? expressions)
      (if (pair? (cdr expressions))
	  (let loop
	      ((expressions expressions)
	       (pointer pointer)
	       (vs '())
	       (kf kf))
	    (bind-delayed-lambdas
	     (lambda (ks)
	       (compile-parser-expression (car expressions) pointer ks kf
					  free-names))
	     (make-parser-ks-lambda
	      (lambda (v kf)
		(let ((vs (cons v vs)))
		  (if (pair? (cdr expressions))
		      (loop (cdr expressions) #f vs kf)
		      (delay-call ks `(VECTOR-APPEND ,@(reverse vs)) kf)))))))
	  (compile-parser-expression (car expressions) pointer ks kf
				     free-names))
      (delay-call ks `(VECTOR) kf)))

(define-parser (alt . expressions)
  (if (pair? expressions)
      (if (pair? (cdr expressions))
	  (let loop ((expressions expressions) (pointer pointer))
	    (if (pair? (cdr expressions))
		(call-with-pointer pointer
		  (lambda (pointer)
		    (bind-delayed-lambdas
		     (lambda (kf)
		       (compile-parser-expression (car expressions)
						  pointer
						  ks
						  kf
						  free-names))
		     (backtracking-kf pointer
		       (lambda ()
			 (loop (cdr expressions) pointer))))))
		(compile-parser-expression (car expressions)
					   pointer
					   ks
					   kf
					   free-names)))
	  (compile-parser-expression (car expressions) ks kf free-names))
      (delay-call kf)))

(define-parser (* expression)
  pointer
  (let ((ks2 (make-ks-identifier))
	(v (make-value-identifier))
	(kf2 (make-kf-identifier)))
    `(LET ,ks2 ((,v (VECTOR)) (,kf2 ,kf))
       ,(call-with-pointer #f
	  (lambda (pointer)
	    (bind-delayed-lambdas
	     (lambda (ks kf)
	       (compile-parser-expression expression pointer ks kf free-names))
	     (make-parser-ks-lambda
	      (lambda (v2 kf)
		(delay-call ks2 `(VECTOR-APPEND ,v ,(delay-reference v2)) kf)))
	     (backtracking-kf pointer
	       (lambda ()
		 (delay-call ks v kf2)))))))))