guile-library 0.2.1-1 / usr / share / guile / site / text / parse-lalr.scm

;; (text parse-lalr) -- yacc's parser generator, in Guile
;; Copyright (C) 1984,1989,1990  Free Software Foundation, Inc.
;; Copyright (C) 1996-2002  Dominique Boucher

;; 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 3 of the License, 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 program.  If not, see <http://www.gnu.org/licenses/>.


;; ---------------------------------------------------------------------- ;;
#!
;;; Commentary:
This file contains yet another LALR(1) parser generator written in     
Scheme. In contrast to other such parser generators, this one          
implements a more efficient algorithm for computing the lookahead sets.
The algorithm is the same as used in Bison (GNU yacc) and is described 
in the following paper:                                                

"Efficient Computation of LALR(1) Look-Ahead Set", F. DeRemer and   
T. Pennello, TOPLAS, vol. 4, no. 4, october 1982.                      

As a consequence, it is not written in a fully functional style.       
In fact, much of the code is a direct translation from C to Scheme     
of the Bison sources.                                                  
                                                                       
@section Defining a parser                                    
                                                                       
The module @code{(text parse-lalr)} declares a macro called @code{lalr-parser}:
@lisp
   (lalr-parser tokens rules ...)                                      
@end lisp
                                                                       
This macro, when given appropriate arguments, generates an LALR(1)     
syntax analyzer.  The macro accepts at least two arguments. The first  
is a list of symbols which represent the terminal symbols of the       
grammar. The remaining arguments are the grammar production rules.
                                                                       
@section Running the parser
                                                                       
The parser generated by the @code{lalr-parser} macro is a function that 
takes two parameters. The first parameter is a lexical analyzer while  
the second is an error procedure.                                      
                                                                       
The lexical analyzer is zero-argument function (a thunk)               
invoked each time the parser needs to look-ahead in the token stream.  
A token is usually a pair whose @code{car} is the symbol corresponding to  
the token (the same symbol as used in the grammar definition). The     
@code{cdr} of the pair is the semantic value associated with the token. For
example, a string token would have the @code{car} set to @code{'string}
while the @code{cdr} is set to the string value @code{"hello"}.      
                                                                       
Once the end of file is encountered, the lexical analyzer must always  
return the symbol @code{'*eoi*} each time it is invoked.                 
                                                                       
The error procedure must be a function that accepts at least two        
parameters.                                                            

@section The grammar format                                 
                                                                       
The grammar is specified by first giving the list of terminals and the 
list of non-terminal definitions. Each non-terminal definition         
is a list where the first element is the non-terminal and the other    
elements are the right-hand sides (lists of grammar symbols). In       
addition to this, each rhs can be followed by a semantic action.       
                                                                       
For example, consider the following (yacc) grammar for a very simple   
expression language:                                                   
@example                                                              
  e : e '+' t                                                          
    | e '-' t                                                          
    | t                                                                
    ;                                                                  
  t : t '*' f                                                          
    : t '/' f                                                          
    | f                                                                
    ;                                                                  
  f : ID                                                               
    ;                                                                  
@end example                                                           
The same grammar, written for the scheme parser generator, would look  
like this (with semantic actions)                                      
@lisp                                                              
(define expr-parser                                                    
  (lalr-parser                                                         
   ; Terminal symbols                                                  
   (ID + - * /)                                                        
   ; Productions                                                       
   (e (e + t)    : (+ $1 $3)                                           
      (e - t)    : (- $1 $3)                                           
      (t)        : $1)                                                 
   (t (t * f)    : (* $1 $3)                                           
      (t / f)    : (/ $1 $3)                                           
      (f)        : $1)                                                 
   (f (ID)       : $1)))                                               
@end lisp                                                           
In semantic actions, the symbol @code{$n} refers to the synthesized        
attribute value of the nth symbol in the production. The value         
associated with the non-terminal on the left is the result of          
evaluating the semantic action (it defaults to @code{#f}).    
                                                                       
The above grammar implicitly handles operator precedences. It is also  
possible to explicitly assign precedences and associativity to         
terminal symbols and productions a la Yacc. Here is a modified    
(and augmented) version of the grammar:                                
@lisp                                                              
(define expr-parser                                                    
 (lalr-parser                                                          
  ; Terminal symbols                                                   
  (ID                                                                  
   (left: + -)                                                         
   (left: * /)                                                         
   (nonassoc: uminus))                                                 
  (e (e + e)              : (+ $1 $3)                                  
     (e - e)              : (- $1 $3)                                  
     (e * e)              : (* $1 $3)                                  
     (e / e)              : (/ $1 $3)                                  
     (- e (prec: uminus)) : (- $2)                                     
     (ID)                 : $1)))                                      
@end lisp                                                           
The @code{left:} directive is used to specify a set of left-associative    
operators of the same precedence level, the @code{right:} directive for    
right-associative operators, and @code{nonassoc:} for operators that       
are not associative. Note the use of the (apparently) useless          
terminal @code{uminus}. It is only defined in order to assign to the       
penultimate rule a precedence level higher than that of @code{*} and  
@code{/}. The @code{prec:} directive can only appear as the last element of a  
rule. Finally, note that precedence levels are incremented from        
left to right, i.e. the precedence level of @code{+} and @code{-} is less     
than the precedence level of @code{*} and @code{/} since the formers appear    
first in the list of terminal symbols (token definitions).             
                                                                       
@section A final note on conflict resolution
                                                                       
Conflicts in the grammar are handled in a conventional way.            
In the absence of precedence directives,                               
Shift/Reduce conflicts are resolved by shifting, and Reduce/Reduce     
conflicts are resolved by choosing the rule listed first in the        
grammar definition.                                                    
                                                                       
You can print the states of the generated parser by evaluating         
@code{(print-states)}. The format of the output is similar to the one      
produced by bison when given the -v command-line option.               
;;; Code:
!#

;;; ---------- SYSTEM DEPENDENT SECTION -----------------
;; put in a module by Richard Todd
(define-module (text parse-lalr)
     #:use-module (scheme documentation)
     #:export (lalr-parser
               print-states))

;; this code is by Thien-Thi Nguyen, found in a google search
(begin
  (defmacro def-macro (form . body)
    `(defmacro ,(car form) ,(cdr form) ,@body))
  (def-macro (BITS-PER-WORD) 28)
  (def-macro (lalr-error msg obj) `(throw 'lalr-error ,msg ,obj))
  (def-macro (logical-or x . y) `(logior ,x ,@y)))

;;; ---------- END OF SYSTEM DEPENDENT SECTION ------------

;; - Macros pour la gestion des vecteurs de bits

(def-macro (set-bit v b)
  `(let ((x (quotient ,b (BITS-PER-WORD)))
	 (y (expt 2 (remainder ,b (BITS-PER-WORD)))))
     (vector-set! ,v x (logical-or (vector-ref ,v x) y))))

(def-macro (bit-union v1 v2 n)
  `(do ((i 0 (+ i 1)))
       ((= i ,n))
     (vector-set! ,v1 i (logical-or (vector-ref ,v1 i) 
				    (vector-ref ,v2 i)))))

;; - Macro pour les structures de donnees

(def-macro (new-core)              `(make-vector 4 0))
(def-macro (set-core-number! c n)  `(vector-set! ,c 0 ,n))
(def-macro (set-core-acc-sym! c s) `(vector-set! ,c 1 ,s))
(def-macro (set-core-nitems! c n)  `(vector-set! ,c 2 ,n))
(def-macro (set-core-items! c i)   `(vector-set! ,c 3 ,i))
(def-macro (core-number c)         `(vector-ref ,c 0))
(def-macro (core-acc-sym c)        `(vector-ref ,c 1))
(def-macro (core-nitems c)         `(vector-ref ,c 2))
(def-macro (core-items c)          `(vector-ref ,c 3))

(def-macro (new-shift)              `(make-vector 3 0))
(def-macro (set-shift-number! c x)  `(vector-set! ,c 0 ,x))
(def-macro (set-shift-nshifts! c x) `(vector-set! ,c 1 ,x))
(def-macro (set-shift-shifts! c x)  `(vector-set! ,c 2 ,x))
(def-macro (shift-number s)         `(vector-ref ,s 0))
(def-macro (shift-nshifts s)        `(vector-ref ,s 1))
(def-macro (shift-shifts s)         `(vector-ref ,s 2))

(def-macro (new-red)                `(make-vector 3 0))
(def-macro (set-red-number! c x)    `(vector-set! ,c 0 ,x))
(def-macro (set-red-nreds! c x)     `(vector-set! ,c 1 ,x))
(def-macro (set-red-rules! c x)     `(vector-set! ,c 2 ,x))
(def-macro (red-number c)           `(vector-ref ,c 0))
(def-macro (red-nreds c)            `(vector-ref ,c 1))
(def-macro (red-rules c)            `(vector-ref ,c 2))



(def-macro (new-set nelem)
  `(make-vector ,nelem 0))


(def-macro (vector-map f v)
  `(let ((vm-n (- (vector-length ,v) 1)))
    (let loop ((vm-low 0) (vm-high vm-n))
      (if (= vm-low vm-high)
	  (vector-set! ,v vm-low (,f (vector-ref ,v vm-low) vm-low))
	  (let ((vm-middle (quotient (+ vm-low vm-high) 2)))
	    (loop vm-low vm-middle)
	    (loop (+ vm-middle 1) vm-high))))))


;; - Constantes
(define STATE-TABLE-SIZE 1009)


;; - Tableaux 
(define rrhs         #f)
(define rlhs         #f)
(define ritem        #f)
(define nullable     #f)
(define derives      #f)
(define fderives     #f)
(define firsts       #f)
(define kernel-base  #f)
(define kernel-end   #f)
(define shift-symbol #f)
(define shift-set    #f)
(define red-set      #f)
(define state-table  #f)
(define acces-symbol #f)
(define reduction-table #f)
(define shift-table  #f)
(define consistent   #f)
(define lookaheads   #f)
(define LA           #f)
(define LAruleno     #f)
(define lookback     #f)
(define goto-map     #f)
(define from-state   #f)
(define to-state     #f)
(define includes     #f)
(define F            #f)
(define action-table #f)

;; - Variables
(define nitems          #f)
(define nrules          #f)
(define nvars           #f)
(define nterms          #f)
(define nsyms           #f)
(define nstates         #f)
(define first-state     #f)
(define last-state      #f)
(define final-state     #f)
(define first-shift     #f)
(define last-shift      #f)
(define first-reduction #f)
(define last-reduction  #f)
(define nshifts         #f)
(define maxrhs          #f)
(define ngotos          #f)
(define token-set-size  #f)

(define (gen-tables! tokens gram)
  (initialize-all)
  (rewrite-grammar 
   tokens
   gram
   (lambda (terms terms/prec vars gram gram/actions)
     (set! the-terminals/prec (list->vector terms/prec))
     (set! the-terminals (list->vector terms))
     (set! the-nonterminals (list->vector vars))
     (set! nterms (length terms))
     (set! nvars  (length vars))
     (set! nsyms  (+ nterms nvars))
     (let ((no-of-rules (length gram/actions))
	   (no-of-items (let loop ((l gram/actions) (count 0))
			  (if (null? l) 
			      count
			      (loop (cdr l) (+ count (length (caar l))))))))
       (pack-grammar no-of-rules no-of-items gram)
       (set-derives)
       (set-nullable)
       (generate-states)
       (lalr)
       (build-tables)
       (compact-action-table terms)
       gram/actions))))


(define (initialize-all)
  (set! rrhs         #f)
  (set! rlhs         #f)
  (set! ritem        #f)
  (set! nullable     #f)
  (set! derives      #f)
  (set! fderives     #f)
  (set! firsts       #f)
  (set! kernel-base  #f)
  (set! kernel-end   #f)
  (set! shift-symbol #f)
  (set! shift-set    #f)
  (set! red-set      #f)
  (set! state-table  (make-vector STATE-TABLE-SIZE '()))
  (set! acces-symbol #f)
  (set! reduction-table #f)
  (set! shift-table  #f)
  (set! consistent   #f)
  (set! lookaheads   #f)
  (set! LA           #f)
  (set! LAruleno     #f)
  (set! lookback     #f)
  (set! goto-map     #f)
  (set! from-state   #f)
  (set! to-state     #f)
  (set! includes     #f)
  (set! F            #f)
  (set! action-table #f)
  (set! nstates         #f)
  (set! first-state     #f)
  (set! last-state      #f)
  (set! final-state     #f)
  (set! first-shift     #f)
  (set! last-shift      #f)
  (set! first-reduction #f)
  (set! last-reduction  #f)
  (set! nshifts         #f)
  (set! maxrhs          #f)
  (set! ngotos          #f)
  (set! token-set-size  #f)
  (set! rule-precedences '()))


(define (pack-grammar no-of-rules no-of-items gram)
  (set! nrules (+  no-of-rules 1))
  (set! nitems no-of-items)
  (set! rlhs (make-vector nrules #f))
  (set! rrhs (make-vector nrules #f))
  (set! ritem (make-vector (+ 1 nitems) #f))

  (let loop ((p gram) (item-no 0) (rule-no 1))
	(if (not (null? p))
	(let ((nt (caar p)))
	  (let loop2 ((prods (cdar p)) (it-no2 item-no) (rl-no2 rule-no))
		(if (null? prods)
		(loop (cdr p) it-no2 rl-no2)
		(begin
		  (vector-set! rlhs rl-no2 nt)
		  (vector-set! rrhs rl-no2 it-no2)
		  (let loop3 ((rhs (car prods)) (it-no3 it-no2))
			(if (null? rhs)
			(begin
			  (vector-set! ritem it-no3 (- rl-no2))
			  (loop2 (cdr prods) (+ it-no3 1) (+ rl-no2 1)))
			(begin
			  (vector-set! ritem it-no3 (car rhs))
			  (loop3 (cdr rhs) (+ it-no3 1))))))))))))


;; Fonction set-derives
;; --------------------
(define (set-derives)
  (define delts (make-vector (+ nrules 1) 0))
  (define dset  (make-vector nvars -1))

  (let loop ((i 1) (j 0))		; i = 0
    (if (< i nrules)
	(let ((lhs (vector-ref rlhs i)))
	  (if (>= lhs 0)
	      (begin
		(vector-set! delts j (cons i (vector-ref dset lhs)))
		(vector-set! dset lhs j)
		(loop (+ i 1) (+ j 1)))
	      (loop (+ i 1) j)))))
  
  (set! derives (make-vector nvars 0))
  
  (let loop ((i 0))
    (if (< i nvars)
	(let ((q (let loop2 ((j (vector-ref dset i)) (s '()))
		   (if (< j 0)
		       s
		       (let ((x (vector-ref delts j)))
			 (loop2 (cdr x) (cons (car x) s)))))))
	  (vector-set! derives i q)
	  (loop (+ i 1))))))



(define (set-nullable)
  (set! nullable (make-vector nvars #f))
  (let ((squeue (make-vector nvars #f))
	(rcount (make-vector (+ nrules 1) 0))
	(rsets  (make-vector nvars #f))
	(relts  (make-vector (+ nitems nvars 1) #f)))
    (let loop ((r 0) (s2 0) (p 0))
      (let ((*r (vector-ref ritem r)))
	(if *r
	    (if (< *r 0)
		(let ((symbol (vector-ref rlhs (- *r))))
		  (if (and (>= symbol 0)
			   (not (vector-ref nullable symbol)))
		      (begin
			(vector-set! nullable symbol #t)
			(vector-set! squeue s2 symbol)
			(loop (+ r 1) (+ s2 1) p))))
		(let loop2 ((r1 r) (any-tokens #f))
		  (let* ((symbol (vector-ref ritem r1)))
		    (if (> symbol 0)
			(loop2 (+ r1 1) (or any-tokens (>= symbol nvars)))
			(if (not any-tokens)
			    (let ((ruleno (- symbol)))
			      (let loop3 ((r2 r) (p2 p))
				(let ((symbol (vector-ref ritem r2)))
				  (if (> symbol 0)
				      (begin
					(vector-set! rcount ruleno
						     (+ (vector-ref rcount ruleno) 1))
					(vector-set! relts p2
						     (cons (vector-ref rsets symbol)
							   ruleno))
					(vector-set! rsets symbol p2)
					(loop3 (+ r2 1) (+ p2 1)))
				      (loop (+ r2 1) s2 p2)))))
			    (loop (+ r1 1) s2 p))))))
	    (let loop ((s1 0) (s3 s2))
	      (if (< s1 s3)
		  (let loop2 ((p (vector-ref rsets (vector-ref squeue s1))) (s4 s3))
		    (if p 
			(let* ((x (vector-ref relts p))
			       (ruleno (cdr x))
			       (y (- (vector-ref rcount ruleno) 1)))
			  (vector-set! rcount ruleno y)
			  (if (= y 0)
			      (let ((symbol (vector-ref rlhs ruleno)))
				(if (and (>= symbol 0)
					 (not (vector-ref nullable symbol)))
				    (begin
				      (vector-set! nullable symbol #t)
				      (vector-set! squeue s4 symbol)
				      (loop2 (car x) (+ s4 1)))
				    (loop2 (car x) s4)))
			      (loop2 (car x) s4))))
		    (loop (+ s1 1) s4)))))))))
		  


; Fonction set-firsts qui calcule un tableau de taille
; nvars et qui donne, pour chaque non-terminal X, une liste des
; non-terminaux pouvant apparaitre au debut d'une derivation a
; partir de X.

(define (set-firsts)
  (set! firsts (make-vector nvars '()))
  
  ;; -- initialization
  (let loop ((i 0))
    (if (< i nvars)
	(let loop2 ((sp (vector-ref derives i)))
	  (if (null? sp)
	      (loop (+ i 1))
	      (let ((sym (vector-ref ritem (vector-ref rrhs (car sp)))))
		(if (< -1 sym nvars)
		    (vector-set! firsts i (sinsert sym (vector-ref firsts i))))
		(loop2 (cdr sp)))))))

  ;; -- reflexive and transitive closure
  (let loop ((continue #t))
    (if continue
	(let loop2 ((i 0) (cont #f))
	  (if (>= i nvars)
	      (loop cont)
	      (let* ((x (vector-ref firsts i))
		     (y (let loop3 ((l x) (z x))
			  (if (null? l)
			      z
			      (loop3 (cdr l)
				     (sunion (vector-ref firsts (car l)) z))))))
		(if (equal? x y)
		    (loop2 (+ i 1) cont)
		    (begin
		      (vector-set! firsts i y)
		      (loop2 (+ i 1) #t))))))))
  
  (let loop ((i 0))
    (if (< i nvars)
	(begin
	  (vector-set! firsts i (sinsert i (vector-ref firsts i)))
	  (loop (+ i 1))))))




; Fonction set-fderives qui calcule un tableau de taille
; nvars et qui donne, pour chaque non-terminal, une liste des regles pouvant
; etre derivees a partir de ce non-terminal. (se sert de firsts)

(define (set-fderives)
  (set! fderives (make-vector nvars #f))

  (set-firsts)

  (let loop ((i 0))
    (if (< i nvars)
	(let ((x (let loop2 ((l (vector-ref firsts i)) (fd '()))
		   (if (null? l) 
		       fd
		       (loop2 (cdr l) 
			      (sunion (vector-ref derives (car l)) fd))))))
	  (vector-set! fderives i x)
	  (loop (+ i 1))))))


; Fonction calculant la fermeture d'un ensemble d'items LR0
; ou core est une liste d'items

(define (closure core)
  ;; Initialization
  (define ruleset (make-vector nrules #f))

  (let loop ((csp core))
    (if (not (null? csp))
	(let ((sym (vector-ref ritem (car csp))))
	  (if (< -1 sym nvars)
	      (let loop2 ((dsp (vector-ref fderives sym)))
		(if (not (null? dsp))
		    (begin
		      (vector-set! ruleset (car dsp) #t)
		      (loop2 (cdr dsp))))))
	  (loop (cdr csp)))))

  (let loop ((ruleno 1) (csp core) (itemsetv '())) ; ruleno = 0
    (if (< ruleno nrules)
	(if (vector-ref ruleset ruleno)
	    (let ((itemno (vector-ref rrhs ruleno)))
	      (let loop2 ((c csp) (itemsetv2 itemsetv))
		(if (and (pair? c)
			 (< (car c) itemno))
		    (loop2 (cdr c) (cons (car c) itemsetv2))
		    (loop (+ ruleno 1) c (cons itemno itemsetv2)))))
	    (loop (+ ruleno 1) csp itemsetv))
	(let loop2 ((c csp) (itemsetv2 itemsetv))
	  (if (pair? c)
	      (loop2 (cdr c) (cons (car c) itemsetv2))
	      (reverse itemsetv2))))))



(define (allocate-item-sets)
  (set! kernel-base (make-vector nsyms 0))
  (set! kernel-end  (make-vector nsyms #f)))


(define (allocate-storage)
  (allocate-item-sets)
  (set! red-set (make-vector (+ nrules 1) 0)))

;; --


(define (initialize-states)
  (let ((p (new-core)))
    (set-core-number! p 0)
    (set-core-acc-sym! p #f)
    (set-core-nitems! p 1)
    (set-core-items! p '(0))

    (set! first-state (list p))
    (set! last-state first-state)
    (set! nstates 1)))



(define (generate-states)
  (allocate-storage)
  (set-fderives)
  (initialize-states)
  (let loop ((this-state first-state))
    (if (pair? this-state)
	(let* ((x (car this-state))
	       (is (closure (core-items x))))
	  (save-reductions x is)
	  (new-itemsets is)
	  (append-states)
	  (if (> nshifts 0)
	      (save-shifts x))
	  (loop (cdr this-state))))))


;; Fonction calculant les symboles sur lesquels il faut "shifter" 
;; et regroupe les items en fonction de ces symboles

(define (new-itemsets itemset)
  ;; - Initialization
  (set! shift-symbol '())
  (let loop ((i 0))
    (if (< i nsyms)
	(begin
	  (vector-set! kernel-end i '())
	  (loop (+ i 1)))))

  (let loop ((isp itemset))
    (if (pair? isp)
	(let* ((i (car isp))
	       (sym (vector-ref ritem i)))
	  (if (>= sym 0)
	      (begin
		(set! shift-symbol (sinsert sym shift-symbol))
		(let ((x (vector-ref kernel-end sym)))
		  (if (null? x)
		      (begin
			(vector-set! kernel-base sym (cons (+ i 1) x))
			(vector-set! kernel-end sym (vector-ref kernel-base sym)))
		      (begin
			(set-cdr! x (list (+ i 1)))
			(vector-set! kernel-end sym (cdr x)))))))
	  (loop (cdr isp)))))

  (set! nshifts (length shift-symbol)))



(define (get-state sym)
  (let* ((isp  (vector-ref kernel-base sym))
	 (n    (length isp))
	 (key  (let loop ((isp1 isp) (k 0))
		 (if (null? isp1)
		     (modulo k STATE-TABLE-SIZE)
		     (loop (cdr isp1) (+ k (car isp1))))))
	 (sp   (vector-ref state-table key)))
    (if (null? sp)
	(let ((x (new-state sym)))
	  (vector-set! state-table key (list x))
	  (core-number x))
	(let loop ((sp1 sp))
	  (if (and (= n (core-nitems (car sp1)))
		   (let loop2 ((i1 isp) (t (core-items (car sp1)))) 
		     (if (and (pair? i1) 
			      (= (car i1)
				 (car t)))
			 (loop2 (cdr i1) (cdr t))
			 (null? i1))))
	      (core-number (car sp1))
	      (if (null? (cdr sp1))
		  (let ((x (new-state sym)))
		    (set-cdr! sp1 (list x))
		    (core-number x))
		  (loop (cdr sp1))))))))


(define (new-state sym)
  (let* ((isp  (vector-ref kernel-base sym))
	 (n    (length isp))
	 (p    (new-core)))
    (set-core-number! p nstates)
    (set-core-acc-sym! p sym)
    (if (= sym nvars) (set! final-state nstates))
    (set-core-nitems! p n)
    (set-core-items! p isp)
    (set-cdr! last-state (list p))
    (set! last-state (cdr last-state))
    (set! nstates (+ nstates 1))
    p))


;; --

(define (append-states)
  (set! shift-set
	(let loop ((l (reverse shift-symbol)))
	  (if (null? l)
	      '()
	      (cons (get-state (car l)) (loop (cdr l)))))))

;; --

(define (save-shifts core)
  (let ((p (new-shift)))
	(set-shift-number! p (core-number core))
	(set-shift-nshifts! p nshifts)
	(set-shift-shifts! p shift-set)
	(if last-shift
	(begin
	  (set-cdr! last-shift (list p))
	  (set! last-shift (cdr last-shift)))
	(begin
	  (set! first-shift (list p))
	  (set! last-shift first-shift)))))

(define (save-reductions core itemset)
  (let ((rs (let loop ((l itemset))
	      (if (null? l)
		  '()
		  (let ((item (vector-ref ritem (car l))))
		    (if (< item 0)
			(cons (- item) (loop (cdr l)))
			(loop (cdr l))))))))
    (if (pair? rs)
	(let ((p (new-red)))
	  (set-red-number! p (core-number core))
	  (set-red-nreds!  p (length rs))
	  (set-red-rules!  p rs)
	  (if last-reduction
	      (begin
		(set-cdr! last-reduction (list p))
		(set! last-reduction (cdr last-reduction)))
	      (begin
		(set! first-reduction (list p))
		(set! last-reduction first-reduction)))))))


;; --

(define (lalr)
  (set! token-set-size (+ 1 (quotient nterms (BITS-PER-WORD))))
  (set-accessing-symbol)
  (set-shift-table)
  (set-reduction-table)
  (set-max-rhs)
  (initialize-LA)
  (set-goto-map)
  (initialize-F)
  (build-relations)
  (digraph includes)
  (compute-lookaheads))

(define (set-accessing-symbol)
  (set! acces-symbol (make-vector nstates #f))
  (let loop ((l first-state))
    (if (pair? l)
	(let ((x (car l)))
	  (vector-set! acces-symbol (core-number x) (core-acc-sym x))
	  (loop (cdr l))))))

(define (set-shift-table)
  (set! shift-table (make-vector nstates #f))
  (let loop ((l first-shift))
    (if (pair? l)
	(let ((x (car l)))
	  (vector-set! shift-table (shift-number x) x)
	  (loop (cdr l))))))

(define (set-reduction-table)
  (set! reduction-table (make-vector nstates #f))
  (let loop ((l first-reduction))
    (if (pair? l)
	(let ((x (car l)))
	  (vector-set! reduction-table (red-number x) x)
	  (loop (cdr l))))))

(define (set-max-rhs)
  (let loop ((p 0) (curmax 0) (length 0))
    (let ((x (vector-ref ritem p)))
      (if x
	  (if (>= x 0)
	      (loop (+ p 1) curmax (+ length 1))
	      (loop (+ p 1) (max curmax length) 0))
	  (set! maxrhs curmax)))))

(define (initialize-LA)
  (define (last l)
    (if (null? (cdr l))
	(car l)
	(last (cdr l))))

  (set! consistent (make-vector nstates #f))
  (set! lookaheads (make-vector (+ nstates 1) #f))

  (let loop ((count 0) (i 0))
    (if (< i nstates)
	(begin
	  (vector-set! lookaheads i count)
	  (let ((rp (vector-ref reduction-table i))
		(sp (vector-ref shift-table i)))
	    (if (and rp
		     (or (> (red-nreds rp) 1)
			 (and sp
			      (not
			       (< (vector-ref acces-symbol
					      (last (shift-shifts sp)))
				  nvars)))))
		(loop (+ count (red-nreds rp)) (+ i 1))
		(begin
		  (vector-set! consistent i #t)
		  (loop count (+ i 1))))))

	(begin
	  (vector-set! lookaheads nstates count)
	  (let ((c (max count 1)))
	    (set! LA (make-vector c #f))
	    (do ((j 0 (+ j 1))) ((= j c)) (vector-set! LA j (new-set token-set-size)))
	    (set! LAruleno (make-vector c -1))
	    (set! lookback (make-vector c #f)))
	  (let loop ((i 0) (np 0))
	    (if (< i nstates)
		(if (vector-ref consistent i)
		    (loop (+ i 1) np)
		    (let ((rp (vector-ref reduction-table i)))
		      (if rp
			  (let loop2 ((j (red-rules rp)) (np2 np))
			    (if (null? j)
				(loop (+ i 1) np2)
				(begin
				  (vector-set! LAruleno np2 (car j))
				  (loop2 (cdr j) (+ np2 1)))))
			  (loop (+ i 1) np))))))))))


(define (set-goto-map)
  (set! goto-map (make-vector (+ nvars 1) 0))
  (let ((temp-map (make-vector (+ nvars 1) 0)))
    (let loop ((ng 0) (sp first-shift))
      (if (pair? sp)
	  (let loop2 ((i (reverse (shift-shifts (car sp)))) (ng2 ng))
	    (if (pair? i)
		(let ((symbol (vector-ref acces-symbol (car i))))
		  (if (< symbol nvars)
		      (begin
			(vector-set! goto-map symbol 
				     (+ 1 (vector-ref goto-map symbol)))
			(loop2 (cdr i) (+ ng2 1)))
		      (loop2 (cdr i) ng2)))
		(loop ng2 (cdr sp))))

	  (let loop ((k 0) (i 0))
	    (if (< i nvars)
		(begin
		  (vector-set! temp-map i k)
		  (loop (+ k (vector-ref goto-map i)) (+ i 1)))

		(begin
		  (do ((i 0 (+ i 1)))
		      ((>= i nvars))
		    (vector-set! goto-map i (vector-ref temp-map i)))

		  (set! ngotos ng)
		  (vector-set! goto-map nvars ngotos)
		  (vector-set! temp-map nvars ngotos)
		  (set! from-state (make-vector ngotos #f))
		  (set! to-state (make-vector ngotos #f))
		  
		  (do ((sp first-shift (cdr sp)))
		      ((null? sp))
		    (let* ((x (car sp))
			   (state1 (shift-number x)))
		      (do ((i (shift-shifts x) (cdr i)))
			  ((null? i))
			(let* ((state2 (car i))
			       (symbol (vector-ref acces-symbol state2)))
			  (if (< symbol nvars)
			      (let ((k (vector-ref temp-map symbol)))
				(vector-set! temp-map symbol (+ k 1))
				(vector-set! from-state k state1)
				(vector-set! to-state k state2))))))))))))))


(define (map-goto state symbol)
  (let loop ((low (vector-ref goto-map symbol))
	     (high (- (vector-ref goto-map (+ symbol 1)) 1)))
    (if (> low high)
	(begin
	  (display (list "Error in map-goto" state symbol) (current-error-port))
          (newline (current-error-port))
	  0)
	(let* ((middle (quotient (+ low high) 2))
	       (s (vector-ref from-state middle)))
	  (cond
	   ((= s state)
	    middle)
	   ((< s state)
	    (loop (+ middle 1) high))
	   (else
	    (loop low (- middle 1))))))))


(define (initialize-F)
  (set! F (make-vector ngotos #f))
  (do ((i 0 (+ i 1))) ((= i ngotos)) (vector-set! F i (new-set token-set-size)))

  (let ((reads (make-vector ngotos #f)))

    (let loop ((i 0) (rowp 0))
      (if (< i ngotos)
	  (let* ((rowf (vector-ref F rowp))
		 (stateno (vector-ref to-state i))
		 (sp (vector-ref shift-table stateno)))
	    (if sp
		(let loop2 ((j (shift-shifts sp)) (edges '()))
		  (if (pair? j)
		      (let ((symbol (vector-ref acces-symbol (car j))))
			(if (< symbol nvars)
			    (if (vector-ref nullable symbol)
				(loop2 (cdr j) (cons (map-goto stateno symbol) 
						     edges))
				(loop2 (cdr j) edges))
			    (begin
			      (set-bit rowf (- symbol nvars))
			      (loop2 (cdr j) edges))))
		      (if (pair? edges)
			  (vector-set! reads i (reverse edges))))))
	      (loop (+ i 1) (+ rowp 1)))))
    (digraph reads)))

(define (add-lookback-edge stateno ruleno gotono)
  (let ((k (vector-ref lookaheads (+ stateno 1))))
    (let loop ((found #f) (i (vector-ref lookaheads stateno)))
      (if (and (not found) (< i k))
	  (if (= (vector-ref LAruleno i) ruleno)
	      (loop #t i)
	      (loop found (+ i 1)))

	  (if (not found)
	      (begin (display "Error in add-lookback-edge : " (current-error-port))
		     (display (list stateno ruleno gotono) (current-error-port))
                     (newline (current-error-port)))
	      (vector-set! lookback i
			   (cons gotono (vector-ref lookback i))))))))


(define (transpose r-arg n)
  (let ((new-end (make-vector n #f))
	(new-R  (make-vector n #f)))
    (do ((i 0 (+ i 1))) 
	((= i n))
      (let ((x (list 'bidon)))
	(vector-set! new-R i x)
	(vector-set! new-end i x)))
    (do ((i 0 (+ i 1)))
	((= i n))
      (let ((sp (vector-ref r-arg i)))
	(if (pair? sp)
	    (let loop ((sp2 sp))
	      (if (pair? sp2)
		  (let* ((x (car sp2))
			 (y (vector-ref new-end x)))
		    (set-cdr! y (cons i (cdr y)))
		    (vector-set! new-end x (cdr y))
		    (loop (cdr sp2))))))))
    (do ((i 0 (+ i 1)))
	((= i n))
      (vector-set! new-R i (cdr (vector-ref new-R i))))
    
    new-R))



(define (build-relations)

  (define (get-state stateno symbol)
    (let loop ((j (shift-shifts (vector-ref shift-table stateno)))
	       (stno stateno))
      (if (null? j)
	  stno
	  (let ((st2 (car j)))
	    (if (= (vector-ref acces-symbol st2) symbol)
		st2
		(loop (cdr j) st2))))))

  (set! includes (make-vector ngotos #f))
  (do ((i 0 (+ i 1)))
      ((= i ngotos))
    (let ((state1 (vector-ref from-state i))
	  (symbol1 (vector-ref acces-symbol (vector-ref to-state i))))
      (let loop ((rulep (vector-ref derives symbol1))
		 (edges '()))
	(if (pair? rulep)
	    (let ((*rulep (car rulep)))
	      (let loop2 ((rp (vector-ref rrhs *rulep))
			  (stateno state1)
			  (states (list state1)))
		(let ((*rp (vector-ref ritem rp)))
		  (if (> *rp 0)
		      (let ((st (get-state stateno *rp)))
			(loop2 (+ rp 1) st (cons st states)))
		      (begin

			(if (not (vector-ref consistent stateno))
			    (add-lookback-edge stateno *rulep i))
			
			(let loop2 ((done #f) 
				    (stp (cdr states))
				    (rp2 (- rp 1))
				    (edgp edges))
			  (if (not done)
			      (let ((*rp (vector-ref ritem rp2)))
				(if (< -1 *rp nvars)
				  (loop2 (not (vector-ref nullable *rp))
					 (cdr stp)
					 (- rp2 1)
					 (cons (map-goto (car stp) *rp) edgp))
				  (loop2 #t stp rp2 edgp)))

			      (loop (cdr rulep) edgp))))))))
	    (vector-set! includes i edges)))))
  (set! includes (transpose includes ngotos)))
			


(define (compute-lookaheads)
  (let ((n (vector-ref lookaheads nstates)))
    (let loop ((i 0))
      (if (< i n)
	  (let loop2 ((sp (vector-ref lookback i)))
	    (if (pair? sp)
		(let ((LA-i (vector-ref LA i))
		      (F-j  (vector-ref F (car sp))))
		  (bit-union LA-i F-j token-set-size)
		  (loop2 (cdr sp)))
		(loop (+ i 1))))))))



(define (digraph relation)
  (define infinity (+ ngotos 2))
  (define INDEX (make-vector (+ ngotos 1) 0))
  (define VERTICES (make-vector (+ ngotos 1) 0))
  (define top 0)
  (define R relation)

  (define (traverse i)
    (set! top (+ 1 top))
    (vector-set! VERTICES top i)
    (let ((height top))
      (vector-set! INDEX i height)
      (let ((rp (vector-ref R i)))
	(if (pair? rp)
	    (let loop ((rp2 rp))
	      (if (pair? rp2)
		  (let ((j (car rp2)))
		    (if (= 0 (vector-ref INDEX j))
			(traverse j))
		    (if (> (vector-ref INDEX i) 
			   (vector-ref INDEX j))
			(vector-set! INDEX i (vector-ref INDEX j)))
		    (let ((F-i (vector-ref F i))
			  (F-j (vector-ref F j)))
		      (bit-union F-i F-j token-set-size))
		    (loop (cdr rp2))))))
	(if (= (vector-ref INDEX i) height)
	    (let loop ()
	      (let ((j (vector-ref VERTICES top)))
		(set! top (- top 1))
		(vector-set! INDEX j infinity)
		(if (not (= i j))
		    (begin
		      (bit-union (vector-ref F i) 
				 (vector-ref F j)
				 token-set-size)
		      (loop)))))))))

  (let loop ((i 0))
    (if (< i ngotos)
	(begin
	  (if (and (= 0 (vector-ref INDEX i))
		   (pair? (vector-ref R i)))
	      (traverse i))
	  (loop (+ i 1))))))


;; ---------------------------------------------------------------------- ;;
;; operator precedence management                                         ;;
;; ---------------------------------------------------------------------- ;;

; a vector of precedence descriptors where each element
; is of the form (terminal type precedence)
(define the-terminals/prec #f)		; terminal symbols with precedence 
; the precedence is an integer >= 0
(define (get-symbol-precedence sym)
  (caddr (vector-ref the-terminals/prec sym)))
; the operator type is either 'none, 'left, 'right, or 'nonassoc
(define (get-symbol-assoc sym)
  (cadr (vector-ref the-terminals/prec sym)))

(define rule-precedences '())
(define (add-rule-precedence! rule sym)
  (set! rule-precedences
	(cons (cons rule sym) rule-precedences)))

(define (get-rule-precedence ruleno)
  (cond
   ((assq ruleno rule-precedences) 
    => (lambda (p) 
	 (get-symbol-precedence (cdr p))))
   (else
    ;; process the rule symbols from left to right
    (let loop ((i    (vector-ref rrhs ruleno))
	       (prec 0))
      (let ((item (vector-ref ritem i)))
	;; end of rule
	(if (< item 0)
	    prec
	    (let ((i1 (+ i 1)))
	      (if (>= item nvars)
		  ;; it's a terminal symbol
		  (loop i1 (get-symbol-precedence (- item nvars)))
		  (loop i1 prec)))))))))

;; ---------------------------------------------------------------------- ;;
;; Build the various tables                                               ;;
;; ---------------------------------------------------------------------- ;;
(define (build-tables)
  
  (define (resolve-conflict sym rule)
    (let ((sym-prec   (get-symbol-precedence sym))
	  (sym-assoc  (get-symbol-assoc sym))
	  (rule-prec  (get-rule-precedence rule)))
      (cond
       ((> sym-prec rule-prec)     'shift)
       ((< sym-prec rule-prec)     'reduce)
       ((eq? sym-assoc 'left)      'reduce)
       ((eq? sym-assoc 'right)     'shift)
       (else                       'shift))))
	
  ;; --- Add an action to the action table ------------------------------ ;;
  (define (add-action St Sym Act)
    (let* ((x (vector-ref action-table St))
	   (y (assv Sym x)))
      (if y
	  (if (not (= Act (cdr y)))
	      ;; -- there is a conflict 
	      (begin
		(if (and (<= (cdr y) 0)
			 (<= Act 0))
		    ;; --- reduce/reduce conflict ----------------------- ;;
		    (begin
		      (display "%% Reduce/Reduce conflict " (current-error-port))
		      (display "(reduce "  (current-error-port))
                      (display (- Act) (current-error-port))
		      (display ", reduce " (current-error-port))
                      (display (- (cdr y)) (current-error-port))
		      (display ") on " (current-error-port))
                      (print-symbol (+ Sym nvars) (current-error-port))
		      (display " in state "  (current-error-port))
                      (display St (current-error-port))
		      (newline (current-error-port))
		      (set-cdr! y (max (cdr y) Act)))
		    ;; --- shift/reduce conflict ------------------------ ;;
		    ;; can we resolve the conflict using precedences?
		    (case (resolve-conflict Sym (- (cdr y)))
		      ;; -- shift
		      ((shift)
		       (set-cdr! y Act))
		      ;; -- reduce
		      ((reduce)
		       #f)		; well, nothing to do...
		      ;; -- signal a conflict!
		      (else
		       (display "%% Shift/Reduce conflict " (current-error-port))
		       (display "(shift " (current-error-port))
                       (display Act (current-error-port))
		       (display ", reduce " (current-error-port))
                       (display (- (cdr y)) (current-error-port))
		       (display ") on " (current-error-port))
                       (print-symbol (+ Sym nvars) (current-error-port))
		       (display " in state " (current-error-port))
                       (display St (current-error-port))
		       (newline (current-error-port))
		       (set-cdr! y Act))))))
	  
	  (vector-set! action-table St (cons (cons Sym Act) x)))))
	
  (set! action-table (make-vector nstates '()))

  (do ((i 0 (+ i 1)))  ; i = state
      ((= i nstates))
    (let ((red (vector-ref reduction-table i)))
      (if (and red (>= (red-nreds red) 1))
	  (if (and (= (red-nreds red) 1) (vector-ref consistent i))
	      (add-action i 'default (- (car (red-rules red))))
	      (let ((k (vector-ref lookaheads (+ i 1))))
		(let loop ((j (vector-ref lookaheads i)))
		  (if (< j k)
		      (let ((rule (- (vector-ref LAruleno j)))
			    (lav  (vector-ref LA j)))
			(let loop2 ((token 0) (x (vector-ref lav 0)) (y 1) (z 0))
			  (if (< token nterms)
			      (begin
				(let ((in-la-set? (modulo x 2)))
				  (if (= in-la-set? 1)
				      (add-action i token rule)))
				(if (= y (BITS-PER-WORD))
				    (loop2 (+ token 1) 
					   (vector-ref lav (+ z 1))
					   1
					   (+ z 1))
				    (loop2 (+ token 1) (quotient x 2) (+ y 1) z)))))
			(loop (+ j 1)))))))))

    (let ((shiftp (vector-ref shift-table i)))
      (if shiftp
	  (let loop ((k (shift-shifts shiftp)))
	    (if (pair? k)
		(let* ((state (car k))
		       (symbol (vector-ref acces-symbol state)))
		  (if (>= symbol nvars)
		      (add-action i (- symbol nvars) state))
		  (loop (cdr k))))))))

  (add-action final-state 0 'accept))

(define (compact-action-table terms)
  (define (most-common-action acts)
    (let ((accums '()))
      (let loop ((l acts))
	(if (pair? l)
	    (let* ((x (cdar l))
		   (y (assv x accums)))
	      (if (and (number? x) (< x 0))
		  (if y
		      (set-cdr! y (+ 1 (cdr y)))
		      (set! accums (cons `(,x . 1) accums))))
	      (loop (cdr l)))))

      (let loop ((l accums) (max 0) (sym #f))
	(if (null? l)
	    sym
	    (let ((x (car l)))
	      (if (> (cdr x) max)
		  (loop (cdr l) (cdr x) (car x))
		  (loop (cdr l) max sym)))))))
  
  (define (translate-terms acts)
    (map (lambda (act) 
	   (cons (list-ref terms (car act))
		 (cdr act)))
	 acts))

  (do ((i 0 (+ i 1)))
      ((= i nstates))
    (let ((acts (vector-ref action-table i)))
      (if (vector? (vector-ref reduction-table i))
	  (let ((act (most-common-action acts)))
	    (vector-set! action-table i
			 (cons `(*default* . ,(if act act 'error))
			       (translate-terms
				(lalr-filter (lambda (x) 
					  (not (eq? (cdr x) act)))
					acts)))))
	  (vector-set! action-table i 
		       (cons `(*default* . *error*) 
			     (translate-terms acts)))))))



;; --

(define (rewrite-grammar tokens grammar k) 

  (define eoi '*eoi*)
  
  (define (check-terminal term terms)
    (cond 
     ((not (valid-terminal? term))
      (lalr-error "invalid terminal: " term))
     ((member term terms)
      (lalr-error "duplicate definition of terminal: " term))))
  
  (define (prec->type prec)
    (cdr (assq prec '((left:     . left) 
		      (right:    . right)
		      (nonassoc: . nonassoc)))))

  (cond
   ;; --- a few error conditions ---------------------------------------- ;;
   ((not (list? tokens))
    (lalr-error "Invalid token list: " tokens))
   ((not (pair? grammar))
    (lalr-error "Grammar definition must have a non-empty list of productions" '()))
   
   (else
    ;; --- check the terminals ---------------------------------------- ;;
    (let loop1 ((lst            tokens)
		(rev-terms      '())
		(rev-terms/prec '())
		(prec-level     0))
      (if (pair? lst)
	  (let ((term (car lst)))
	    (cond
	     ((pair? term)
	      (if (and (memq (car term) '(left: right: nonassoc:))
		       (not (null? (cdr term))))
		  (let ((prec    (+ prec-level 1))
			(optype  (prec->type (car term))))
		    (let loop-toks ((l             (cdr term))
				    (rev-terms      rev-terms)
				    (rev-terms/prec rev-terms/prec))
		      (if (null? l)
			  (loop1 (cdr lst) rev-terms rev-terms/prec prec)
			  (let ((term (car l)))
			    (check-terminal term rev-terms)
			    (loop-toks 
			     (cdr l)
			     (cons term rev-terms)
			     (cons (list term optype prec) rev-terms/prec))))))
		  
		  (lalr-error "invalid operator precedence specification: " term)))
	      
	     (else
	      (check-terminal term rev-terms)
	      (loop1 (cdr lst) 
		     (cons term rev-terms)
		     (cons (list term 'none 0) rev-terms/prec)
		     prec-level))))
	  
	  ;; --- check the grammar rules ------------------------------ ;;
	  (let loop2 ((lst grammar) (rev-nonterm-defs '()))
	    (if (pair? lst)
		(let ((def (car lst)))
		  (if (not (pair? def))
		      (lalr-error "Nonterminal definition must be a non-empty list" '())
		      (let ((nonterm (car def)))
			(cond ((not (valid-nonterminal? nonterm))
			       (lalr-error "Invalid nonterminal:" nonterm))
			      ((or (member nonterm rev-terms)
				   (assoc nonterm rev-nonterm-defs))
			       (lalr-error "Nonterminal previously defined:" nonterm))
			      (else
			       (loop2 (cdr lst)
				      (cons def rev-nonterm-defs)))))))
		(let* ((terms        (cons eoi (reverse rev-terms)))
		       (terms/prec   (cons '(eoi none 0) (reverse rev-terms/prec)))
		       (nonterm-defs (reverse rev-nonterm-defs))
		       (nonterms     (cons '*start* (map car nonterm-defs))))
		  (if (= (length nonterms) 1)
		      (lalr-error "Grammar must contain at least one nonterminal" '())
		      (let loop-defs ((defs      (cons `(*start* (,(cadr nonterms) ,eoi) : $1)
						       nonterm-defs))
				      (ruleno    0)
				      (comp-defs '()))
			(if (pair? defs)
			    (let* ((nonterm-def  (car defs))
				   (compiled-def (rewrite-nonterm-def 
						  nonterm-def 
						  ruleno
						  terms nonterms)))
			      (loop-defs (cdr defs)
					 (+ ruleno (length compiled-def))
					 (cons compiled-def comp-defs)))

			    (let ((compiled-nonterm-defs (reverse comp-defs)))
			      (k terms
				 terms/prec
				 nonterms
				 (map (lambda (x) (cons (caaar x) (map cdar x)))
				      compiled-nonterm-defs)
				 (apply append compiled-nonterm-defs))))))))))))))


(define (rewrite-nonterm-def nonterm-def ruleno terms nonterms)

  (define No-NT (length nonterms))

  (define (encode x) 
    (let ((PosInNT (pos-in-list x nonterms)))
      (if PosInNT
	  PosInNT
	  (let ((PosInT (pos-in-list x terms)))
	    (if PosInT
		(+ No-NT PosInT)
		(lalr-error "undefined symbol : " x))))))
  
  (define (process-prec-directive rhs ruleno)
    (let loop ((l rhs))
      (if (null? l) 
	  '()
	  (let ((first (car l))
		(rest  (cdr l)))
	    (cond
	     ((or (member first terms) (member first nonterms))
	      (cons first (loop rest)))
	     ((and (pair? first)
		   (eq? (car first) 'prec:))
		   (pair? (cdr first))
	      (if (and (pair? (cdr first))
		       (member (cadr first) terms))
		  (if (null? (cddr first))
		      (begin
			(add-rule-precedence! ruleno (pos-in-list (cadr first) terms))
			(loop rest))
		      (lalr-error "prec: directive should be at end of rule: " rhs))
		  (lalr-error "Invalid prec: directive: " first)))
	     (else
	      (lalr-error "Invalid terminal or nonterminal: " first)))))))
	

  (if (not (pair? (cdr nonterm-def)))
      (lalr-error "At least one production needed for nonterminal" (car nonterm-def))
      (let ((name (symbol->string (car nonterm-def))))
	(let loop1 ((lst (cdr nonterm-def))
		    (i 1)
		    (rev-productions-and-actions '()))
	  (if (not (pair? lst))
	      (reverse rev-productions-and-actions)
	      (let* ((rhs  (process-prec-directive (car lst) (+ ruleno i -1)))
		     (rest (cdr lst))
		     (prod (map encode (cons (car nonterm-def) rhs))))
		(for-each (lambda (x)
			    (if (not (or (member x terms) (member x nonterms)))
				(lalr-error "Invalid terminal or nonterminal" x)))
			  rhs)
		(if (and (pair? rest)
			 (eq? (car rest) ':)
			 (pair? (cdr rest)))
		    (loop1 (cddr rest)
			   (+ i 1)
			   (cons (cons prod (cadr rest)) 
				 rev-productions-and-actions))
		    (let* ((rhs-length (length rhs))
			   (action
			    (cons 'vector
				 (cons (list 'quote (string->symbol
						     (string-append
						      name
						      "-"
						      (number->string i))))
				       (let loop-j ((j 1))
					 (if (> j rhs-length)
					     '()
					     (cons (string->symbol
						    (string-append
						     "$"
						     (number->string j)))
						   (loop-j (+ j 1)))))))))
		      (loop1 rest
			     (+ i 1)
			     (cons (cons prod action) 
				   rev-productions-and-actions))))))))))

(define (valid-nonterminal? x)
  (symbol? x))

(define (valid-terminal? x)
  (symbol? x))              ; DB 

;; ---------------------------------------------------------------------- ;;
;; Miscellaneous                                                          ;;
;; ---------------------------------------------------------------------- ;;
(define (pos-in-list x lst)
  (let loop ((lst lst) (i 0))
    (cond ((not (pair? lst))    #f)
	  ((equal? (car lst) x) i)
	  (else                 (loop (cdr lst) (+ i 1))))))

(define (sunion lst1 lst2)		; union of sorted lists
  (let loop ((L1 lst1)
	     (L2 lst2))
    (cond ((null? L1)    L2)
	  ((null? L2)    L1)
	  (else 
	   (let ((x (car L1)) (y (car L2)))
	     (cond
	      ((> x y)
	       (cons y (loop L1 (cdr L2))))
	      ((< x y)
	       (cons x (loop (cdr L1) L2)))
	      (else
	       (loop (cdr L1) L2))
	      ))))))

(define (sinsert elem lst)
  (let loop ((l1 lst))
    (if (null? l1) 
	(cons elem l1)
	(let ((x (car l1)))
	  (cond ((< elem x)
		 (cons elem l1))
		((> elem x)
		 (cons x (loop (cdr l1))))
		(else 
		 l1))))))

(define (lalr-filter p lst)
  (let loop ((l lst))
    (if (null? l)
	'()
	(let ((x (car l)) (y (cdr l)))
	(if (p x)
	    (cons x (loop y))
	    (loop y))))))

;; ---------------------------------------------------------------------- ;;
;; Debugging tools ...                                                    ;;
;; ---------------------------------------------------------------------- ;;
(define the-terminals #f)		; names of terminal symbols
(define the-nonterminals #f)		; non-terminals

(define (print-item item-no)
  (let loop ((i item-no))
    (let ((v (vector-ref ritem i)))
      (if (>= v 0)
	  (loop (+ i 1))
	  (let* ((rlno    (- v))
		 (nt      (vector-ref rlhs rlno)))
	    (display (vector-ref the-nonterminals nt)) (display " --> ")
	    (let loop ((i (vector-ref rrhs rlno)))
	      (let ((v (vector-ref ritem i)))
		(if (= i item-no)
		    (display ". "))
		(if (>= v 0)
		    (begin
		      (print-symbol v)
		      (display " ")
		      (loop (+ i 1)))
		    (begin 
		      (display "   (rule ")
		      (display (- v))
		      (display ")")
		      (newline))))))))))
  
(define (print-symbol n . port)
  (display (if (>= n nvars)
	       (vector-ref the-terminals (- n nvars))
	       (vector-ref the-nonterminals n))
           (if (null? port)
               (current-output-port)
               (car port))))
  
(define (print-states)
"Print the states of a generated parser."
  (define (print-action act)
    (cond
     ((eq? act '*error*)
      (display " : Error"))
     ((eq? act 'accept)
      (display " : Accept input"))
     ((< act 0)
      (display " : reduce using rule ")
      (display (- act)))
     (else
      (display " : shift and goto state ")
      (display act)))
    (newline)
    #t)
  
  (define (print-actions acts)
    (let loop ((l acts))
      (if (null? l)
	  #t
	  (let ((sym (caar l))
		(act (cdar l)))
	    (display "   ")
	    (cond
	     ((eq? sym 'default)
	      (display "default action"))
	     (else
	      (if (number? sym)
		  (print-symbol (+ sym nvars))
		  (display sym))))
	    (print-action act)
	    (loop (cdr l))))))
  
  (if (not action-table)
      (begin
	(display "No generated parser available!")
	(newline)
	#f)
      (begin
	(display "State table") (newline)
	(display "-----------") (newline) (newline)
  
	(let loop ((l first-state))
	  (if (null? l)
	      #t
	      (let* ((core  (car l))
		     (i     (core-number core))
		     (items (core-items core))
		     (actions (vector-ref action-table i)))
		(display "state ") (display i) (newline)
		(newline)
		(for-each (lambda (x) (display "   ") (print-item x))
			  items)
		(newline)
		(print-actions actions)
		(newline)
		(loop (cdr l))))))))


	  
;; ---------------------------------------------------------------------- ;;

(define build-goto-table
  (lambda ()
    `(vector
      ,@(map
	 (lambda (shifts)
	   (list 'quote
		 (if shifts
		     (let loop ((l (shift-shifts shifts)))
		       (if (null? l)
			   '()
			   (let* ((state  (car l))
				  (symbol (vector-ref acces-symbol state)))
			     (if (< symbol nvars)
				 (cons `(,symbol . ,state)
				       (loop (cdr l)))
				 (loop (cdr l))))))
		     '())))
	 (vector->list shift-table)))))


(define build-reduction-table
  (lambda (gram/actions)
    `(vector
      '()
      ,@(map
	 (lambda (p)
	   (let ((act (cdr p)))
	     `(lambda (___stack ___sp ___goto-table ___k)
		,(let* ((nt (caar p)) (rhs (cdar p)) (n (length rhs)))
		   `(let* (,@(if act
				 (let loop ((i 1) (l rhs))
				   (if (pair? l)
				       (let ((rest (cdr l)))
					 (cons 
					  `(,(string->symbol
					      (string-append
					       "$"
					       (number->string 
						(+ (- n i) 1))))
					    (vector-ref ___stack (- ___sp ,(- (* i 2) 1))))
					  (loop (+ i 1) rest)))
				       '()))
				 '()))
		      ,(if (= nt 0)
			   '$1
			   `(___push ___stack (- ___sp ,(* 2 n)) 
				  ,nt ___goto-table ,(cdr p) ___k)))))))

	 gram/actions))))
	 

;; @section (api "API")                                                   

(define-macro-with-docs (lalr-parser tokens . rules)
"The grammar declaration special form.  @var{tokens} is the list of token
symbols, and @var{rules} are the grammar rules.  See the module documentation
for more details."
  (let* ((gram/actions (gen-tables! tokens rules))
	 (code
	  `(letrec ((___max-stack-size 500)

		    (___atable         ',action-table)
		    (___gtable         ,(build-goto-table))
		    (___grow-stack     (lambda (stack)
					 ;; make a new stack twice as big as the original
					 (let ((new-stack (make-vector (* 2 (vector-length stack)) #f)))
					   ;; then copy the elements...
					   (let loop ((i (- (vector-length stack) 1)))
					     (if (< i 0)
						 new-stack
						 (begin
						   (vector-set! new-stack i (vector-ref stack i))
						   (loop (- i 1))))))))
	      
		    (___push           (lambda (stack sp new-cat goto-table lval k)
					 (let* ((state     (vector-ref stack sp))
						(new-state (cdr (assq new-cat (vector-ref goto-table state))))
						(new-sp    (+ sp 2))
						(stack     (if (< new-sp (vector-length stack))
							       stack
							       (___grow-stack stack))))
					   (vector-set! stack new-sp new-state)
					   (vector-set! stack (- new-sp 1) lval)
					   (k stack new-sp))))

		    (___action         (lambda (x l)
					 (let ((y (assq x l)))
					   (if y (cdr y) (cdar l)))))
	      
		    (___rtable         ,(build-reduction-table gram/actions)))

	     (lambda (lexerp errorp)

	       (let ((stack (make-vector ___max-stack-size 0)))
		 (let loop ((stack stack) (sp 0) (input (lexerp)))
		   (let* ((state (vector-ref stack sp))
			  (i     (if (pair? input) (car input) input))
			  (attr  (if (pair? input) (cdr input) #f))
			  (act   (___action i (vector-ref ___atable state))))

		     (if (not (symbol? i))
			 (errorp "PARSE ERROR: invalid token: " input))
		 
		     (cond
		  
		      ;; Input succesfully parsed
		      ((eq? act 'accept)
		       (vector-ref stack 1))
		  
		      ;; Syntax error in input
		      ((eq? act '*error*)
		       (if (eq? i '*eoi*)
			   (errorp "PARSE ERROR : unexpected end of input ")
			   (errorp "PARSE ERROR : unexpected token : " input)))
		  
		      ;; Shift current token on top of the stack
		      ((>= act 0)
		       (let ((stack (if (< (+ sp 2) (vector-length stack))
					stack
					(___grow-stack stack))))
			 (vector-set! stack (+ sp 1) attr)
			 (vector-set! stack (+ sp 2) act)
			 (loop stack (+ sp 2) (lexerp))))

		      ;; Reduce by rule (- act)
		      (else 
		       ((vector-ref ___rtable (- act))
			stack sp ___gtable
			(lambda (stack sp)
			  (loop stack sp input))))))))))))
    code))

;; arch-tag: 4FE771DE-F56D-11D8-8B77-000A95B4C7DC