#lang racket/base (require yaragg/parser-tools/private-yacc/lr0 yaragg/parser-tools/private-yacc/grammar racket/class racket/list) ;; Compute LALR lookaheads from DeRemer and Pennello 1982 (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) tk) (define r (send a run-automaton (trans-key-st tk) (trans-key-gs tk))) (term-list->bit-vector (filter (λ (term) (send a run-automaton r term)) (grammar-terms g)))) ;; compute-reads: ;; LR0-automaton * grammar -> (trans-key -> trans-key list) (define (compute-reads a g) (define nullable-non-terms (filter (λ (nt) (grammar-nullable-non-term? g nt)) (grammar-non-terms g))) (λ (tk) (define r (send a run-automaton (trans-key-st tk) (trans-key-gs tk))) (for/list ([non-term (in-list nullable-non-terms)] #:when (send a run-automaton r non-term)) (trans-key r non-term)))) ;; compute-read: LR0-automaton * grammar -> (trans-key -> term set) ;; output term set is represented in bit-vector form (define (compute-read a g) (define dr (compute-DR a g)) (define reads (compute-reads a g)) (digraph-tk->terml (send a get-mapped-non-term-keys) reads dr (send a get-num-states))) ;; 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) (define rhs (prod-rhs prod)) (define rhs-l (vector-length rhs)) (append (if (and (> rhs-l 0) (eq? nt (vector-ref rhs (sub1 rhs-l)))) (list (item prod (sub1 rhs-l))) '()) (let loop ([i (sub1 rhs-l)]) (cond [(and (> i 0) (non-term? (vector-ref rhs i)) (grammar-nullable-non-term? g (vector-ref rhs i))) (if (eq? nt (vector-ref rhs (sub1 i))) (cons (item prod (sub1 i)) (loop (sub1 i))) (loop (sub1 i)))] [else '()])))) ;; 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) (append-map (λ (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) (define num-states (send a get-num-states)) (define items-for-input-nt (make-vector (grammar-num-non-terms g) '())) (for ([input-nt (in-list (grammar-non-terms g))]) (vector-set! items-for-input-nt (non-term-index input-nt) (prod-list->items-for-include g (grammar-all-prods g) input-nt))) (λ (tk) (define goal-state (trans-key-st tk)) (define non-term (trans-key-gs tk)) (define items (vector-ref items-for-input-nt (non-term-index non-term))) (trans-key-list-remove-dups (apply append (for/list ([item (in-list items)]) (define prod (item-prod item)) (define rhs (prod-rhs prod)) (define lhs (prod-lhs prod)) (map (λ (state) (trans-key state lhs)) (run-lr0-backward a rhs (item-dot-pos item) goal-state num-states))))))) ;; compute-lookback: lr0-automaton * grammar -> (kernel * proc -> trans-key list) (define (compute-lookback a g) (define num-states (send a get-num-states)) (λ (state prod) (map (λ (k) (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) (define read (compute-read a g)) (digraph-tk->terml (send a get-mapped-non-term-keys) includes read (send a get-num-states))) ;; compute-LA: LR0-automaton * grammar -> kernel * prod -> term set ;; output term set is represented in bit-vector form (define (compute-LA a g) (define includes (compute-includes a g)) (define lookback (compute-lookback a g)) (define follow (compute-follow a g includes)) (λ (k p) (define l (lookback k p)) (define 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 (λ (state) (for ([non-term (in-list (grammar-non-terms g))]) (define res (f (trans-key state non-term))) (unless (null? res) (printf "~a(~a, ~a) = ~a\n" name state (gram-sym-symbol non-term) (print-output res)))))) (newline)) (define (print-input-st-prod f name a g print-output) (printf "~a:\n" name) (send a for-each-state (λ (state) (for* ([non-term (in-list (grammar-non-terms g))] [prod (in-list (grammar-prods-for-non-term g non-term))]) (define res (f state prod)) (unless (null? res) (printf "~a(~a, ~a) = ~a\n" name (kernel-index state) (prod-index prod) (print-output res))))))) (define (print-output-terms r) (map gram-sym-symbol r)) (define (print-output-st-nt r) (map (λ (p) (list (kernel-index (trans-key-st p)) (gram-sym-symbol (trans-key-gs p)))) r)) ;; init-tk-map : int -> (vectorof hashtable?) (define (init-tk-map n) (define v (make-vector n #f)) (let loop ([i (sub1 (vector-length v))]) (when (>= i 0) (vector-set! v i (make-hasheq)) (loop (sub1 i)))) v) ;; lookup-tk-map : (vectorof (symbol? int hashtable)) -> trans-key? -> int (define ((lookup-tk-map map) tk) (define st (trans-key-st tk)) (define gs (trans-key-gs tk)) (hash-ref (vector-ref map (kernel-index st)) (gram-sym-symbol gs) 0)) ;; add-tk-map : (vectorof (symbol? int hashtable)) -> trans-key int -> (define ((add-tk-map map) tk v) (define st (trans-key-st tk)) (define gs (trans-key-gs tk)) (hash-set! (vector-ref map (kernel-index st)) (gram-sym-symbol gs) v)) ;; 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.rkt (define (digraph-tk->terml nodes edges f- num-states) ;; Will map elements of trans-key to term sets represented as bit vectors (define results (init-tk-map num-states)) ;; Maps elements of trans-keys to integers. (define N (init-tk-map num-states)) (define get-N (lookup-tk-map N)) (define set-N (add-tk-map N)) (define get-f (lookup-tk-map results)) (define set-f (add-tk-map results)) (define stack '()) (define (push x) (set! stack (cons x stack))) (define (pop) (begin0 (car stack) (set! stack (cdr stack)))) (define (depth) (length stack)) ;; traverse: 'a -> (define (traverse x) (push x) (let ([d (depth)]) (set-N x d) (set-f x (f- x)) (for ([y (in-list (edges x))]) (when (= 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)))) (when (= d (get-N x)) (let loop ([p (pop)]) (set-N p +inf.0) (set-f p (get-f x)) (unless (equal? x p) (loop (pop))))))) (for ([x (in-list nodes)] #:when (zero? (get-N x))) (traverse x)) get-f)