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br-parser-tools/collects/parser-tools/private-yacc/lalr.ss

280 lines
10 KiB
Scheme

(module lalr mzscheme
;; Compute LALR lookaheads from DeRemer and Pennello 1982
(require "lr0.ss"
"grammar.ss"
"array2d.ss"
"graph.ss"
(lib "list.ss")
(lib "class.ss"))
(provide compute-LA)
;; compute-DR: LR0-automaton * grammar -> (trans-key -> term set)
;; computes for each state, non-term transition pair, the terminals
;; which can transition out of the resulting state
;; output term set is represented in bit-vector form
(define (compute-DR a g)
(lambda (tk)
(let ((r (send a run-automaton (trans-key-st tk) (trans-key-gs tk))))
(term-list->bit-vector
(filter
(lambda (term)
(send a run-automaton r term))
(send g get-terms))))))
;; compute-reads:
;; LR0-automaton * grammar -> (trans-key -> trans-key list)
(define (compute-reads a g)
(let ((nullable-non-terms
(filter (lambda (nt) (send g nullable-non-term? nt))
(send g get-non-terms))))
(lambda (tk)
(let ((r (send a run-automaton (trans-key-st tk) (trans-key-gs tk))))
(map (lambda (x) (make-trans-key r x))
(filter (lambda (non-term) (send a run-automaton r non-term))
nullable-non-terms))))))
;; compute-read: LR0-automaton * grammar -> (trans-key -> term set)
;; output term set is represented in bit-vector form
(define (compute-read a g)
(let* ((dr (compute-DR a g))
(reads (compute-reads a g)))
(digraph-tk->terml (send a get-mapped-non-term-keys)
reads
dr
(send a get-num-states)
(send g get-num-terms)
(send g get-num-non-terms))))
;; returns the list of all k such that state k transitions to state start on the
;; transitions in rhs (in order)
(define (run-lr0-backward a rhs dot-pos start num-states)
(let loop ((states (list start))
(i (sub1 dot-pos)))
(cond
((< i 0) states)
(else (loop (send a run-automaton-back states (vector-ref rhs i))
(sub1 i))))))
;; prod->items-for-include: grammar * prod * non-term -> lr0-item list
;; returns the list of all (B -> beta . nt gamma) such that prod = (B -> beta nt gamma)
;; and gamma =>* epsilon
(define (prod->items-for-include g prod nt)
(let* ((rhs (prod-rhs prod))
(rhs-l (vector-length rhs)))
(append (if (and (> rhs-l 0) (eq? nt (vector-ref rhs (sub1 rhs-l))))
(list (make-item prod (sub1 rhs-l)))
null)
(let loop ((i (sub1 rhs-l)))
(cond
((and (> i 0)
(non-term? (vector-ref rhs i))
(send g nullable-non-term? (vector-ref rhs i)))
(if (eq? nt (vector-ref rhs (sub1 i)))
(cons (make-item prod (sub1 i))
(loop (sub1 i)))
(loop (sub1 i))))
(else null))))))
;; prod-list->items-for-include: grammar * prod list * non-term -> lr0-item list
;; return the list of all (B -> beta . nt gamma) such that (B -> beta nt gamma) in prod-list
;; and gamma =>* epsilon
(define (prod-list->items-for-include g prod-list nt)
(apply append (map (lambda (prod) (prod->items-for-include g prod nt)) prod-list)))
;; comput-includes: lr0-automaton * grammar -> (trans-key -> trans-key list)
(define (compute-includes a g)
(let ((num-states (send a get-num-states))
(items-for-input-nt (make-vector (send g get-num-non-terms) null)))
(for-each
(lambda (input-nt)
(vector-set! items-for-input-nt (non-term-index input-nt)
(prod-list->items-for-include g (send g get-prods) input-nt)))
(send g get-non-terms))
(lambda (tk)
(let* ((goal-state (trans-key-st tk))
(non-term (trans-key-gs tk))
(items (vector-ref items-for-input-nt (non-term-index non-term))))
(trans-key-list-remove-dups
(apply append
(map (lambda (item)
(let* ((prod (item-prod item))
(rhs (prod-rhs prod))
(lhs (prod-lhs prod)))
(map (lambda (state)
(make-trans-key state lhs))
(run-lr0-backward a
rhs
(item-dot-pos item)
goal-state
num-states))))
items)))))))
;; compute-lookback: lr0-automaton * grammar -> (kernel * proc -> trans-key list)
(define (compute-lookback a g)
(let ((num-states (send a get-num-states)))
(lambda (state prod)
(map (lambda (k) (make-trans-key k (prod-lhs prod)))
(run-lr0-backward a (prod-rhs prod) (vector-length (prod-rhs prod)) state num-states)))))
;; compute-follow: LR0-automaton * grammar -> (trans-key -> term set)
;; output term set is represented in bit-vector form
(define (compute-follow a g includes)
(let ((read (compute-read a g)))
(digraph-tk->terml (send a get-mapped-non-term-keys)
includes
read
(send a get-num-states)
(send g get-num-terms)
(send g get-num-non-terms))))
;; compute-LA: LR0-automaton * grammar -> (kernel * prod -> term set)
;; output term set is represented in bit-vector form
(define (compute-LA a g)
(let* ((includes (compute-includes a g))
(lookback (compute-lookback a g))
(follow (compute-follow a g includes)))
(lambda (k p)
(let* ((l (lookback k p))
(f (map follow l)))
(apply bitwise-ior (cons 0 f))))))
(define (print-DR dr a g)
(print-input-st-sym dr "DR" a g print-output-terms))
(define (print-Read Read a g)
(print-input-st-sym Read "Read" a g print-output-terms))
(define (print-includes i a g)
(print-input-st-sym i "includes" a g print-output-st-nt))
(define (print-lookback l a g)
(print-input-st-prod l "lookback" a g print-output-st-nt))
(define (print-follow f a g)
(print-input-st-sym f "follow" a g print-output-terms))
(define (print-LA l a g)
(print-input-st-prod l "LA" a g print-output-terms))
(define (print-input-st-sym f name a g print-output)
(printf "~a:~n" name)
(send a for-each-state
(lambda (state)
(for-each
(lambda (non-term)
(let ((res (f (make-trans-key state non-term))))
(if (not (null? res))
(printf "~a(~a, ~a) = ~a~n"
name
state
(gram-sym-symbol non-term)
(print-output res)))))
(send g get-non-terms))))
(newline))
(define (print-input-st-prod f name a g print-output)
(printf "~a:~n" name)
(send a for-each-state
(lambda (state)
(for-each
(lambda (non-term)
(for-each
(lambda (prod)
(let ((res (f state prod)))
(if (not (null? res))
(printf "~a(~a, ~a) = ~a~n"
name
(kernel-index state)
(prod-index prod)
(print-output res)))))
(send g get-prods-for-non-term non-term)))
(send g get-non-terms)))))
(define (print-output-terms r)
(map
(lambda (p)
(gram-sym-symbol p))
r))
(define (print-output-st-nt r)
(map
(lambda (p)
(list
(kernel-index (trans-key-st p))
(gram-sym-symbol (trans-key-gs p))))
r))
;; digraph-tk->terml:
;; (trans-key list) * (trans-key -> trans-key list) * (trans-key -> term list) * int * int * int
;; -> (trans-key -> term list)
;; DeRemer and Pennello 1982
;; Computes (f x) = (f- x) union Union{(f y) | y in (edges x)}
;; A specialization of digraph in the file graph.ss
(define (digraph-tk->terml nodes edges f- num-states num-terms num-non-terms)
(letrec (
;; Will map elements of trans-key to term sets represented as bit vectors
(results-terms (make-array2d num-states num-terms 0))
(results-non-terms (make-array2d num-states num-non-terms 0))
;; Maps elements of trans-keys to integers.
(N-terms (make-array2d num-states num-terms 0))
(N-non-terms (make-array2d num-states num-non-terms 0))
(lookup-tk-map
(lambda (map-term map-non-term)
(lambda (tk)
(let ((st (trans-key-st tk))
(gs (trans-key-gs tk)))
(if (term? gs)
(array2d-ref map-term (kernel-index st) (term-index gs))
(array2d-ref map-non-term (kernel-index st) (non-term-index gs)))))))
(add-tk-map
(lambda (map-term map-non-term)
(lambda (tk v)
(let ((st (trans-key-st tk))
(gs (trans-key-gs tk)))
(if (term? gs)
(array2d-set! map-term (kernel-index st) (term-index gs) v)
(array2d-set! map-non-term (kernel-index st) (non-term-index gs) v))))))
(get-N (lookup-tk-map N-terms N-non-terms))
(set-N (add-tk-map N-terms N-non-terms))
(get-f (lookup-tk-map results-terms results-non-terms))
(set-f (add-tk-map results-terms results-non-terms))
(stack null)
(push (lambda (x)
(set! stack (cons x stack))))
(pop (lambda ()
(begin0
(car stack)
(set! stack (cdr stack)))))
(depth (lambda () (length stack)))
;; traverse: 'a ->
(traverse
(lambda (x)
(push x)
(let ((d (depth)))
(set-N x d)
(set-f x (f- x))
(for-each (lambda (y)
(if (= 0 (get-N y))
(traverse y))
(set-f x (bitwise-ior (get-f x) (get-f y)))
(set-N x (min (get-N x) (get-N y))))
(edges x))
(if (= d (get-N x))
(let loop ((p (pop)))
(set-N p +inf.0)
(set-f p (get-f x))
(if (not (equal? x p))
(loop (pop)))))))))
(for-each (lambda (x)
(if (= 0 (get-N x))
(traverse x)))
nodes)
get-f))
)