114 lines
2.3 KiB
C
114 lines
2.3 KiB
C
/*
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* (c) copyright 1987 by the Vrije Universiteit, Amsterdam, The Netherlands.
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* See the copyright notice in the ACK home directory, in the file "Copyright".
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*
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*/
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/*
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* L L G E N
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*
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* An Extended LL(1) Parser Generator
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*
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* Author : Ceriel J.H. Jacobs
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*/
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/*
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* reach.c
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* Determine which nonterminals are reachable, and also check that they
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* are all defined.
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*/
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# include "types.h"
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# include "extern.h"
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# include "io.h"
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# include "assert.h"
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# ifndef NORCSID
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static string rcsid8 = "$Header$";
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# endif
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/* In this file the following routines are defined: */
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extern co_reach();
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STATIC reachable();
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STATIC reachwalk();
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co_reach() {
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/*
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* Check for undefined or unreachable nonterminals.
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* An undefined nonterminal is a fatal error!
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*/
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register p_nont p;
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register p_start st;
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register p_file x;
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register p_order s;
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/* Check for undefined nonterminals */
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for (p = nonterms; p < maxnt; p++) {
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if (! p->n_rule) { /* undefined */
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f_input = p->n_string;
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error(p->n_lineno,"Nonterminal %s not defined",
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p->n_name);
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}
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}
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/*
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* Walk the grammar rules, starting with the startsymbols
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* Mark the nonterminals that are encountered with the flag
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* REACHABLE, and walk their rules, if not done before
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*/
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for (st = start; st; st = st->ff_next) {
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reachable(&nonterms[st->ff_nont]);
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}
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/*
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* Now check for unreachable nonterminals
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*/
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for (x = files; x < maxfiles; x++) {
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f_input = x->f_name;
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for (s = x->f_list; s; s = s->o_next) {
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p = &nonterms[s->o_index];
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if (! (p->n_flags & REACHABLE)) {
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warning(p->n_lineno,"nonterminal %s unreachable",
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p->n_name);
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}
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}
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}
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}
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STATIC
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reachable(p) register p_nont p; {
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/*
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* Enter the fact that p is reachable, and look for implications
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*/
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if (! (p->n_flags & REACHABLE)) {
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p->n_flags |= REACHABLE;
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/*
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* Now walk its grammar rule
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*/
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if (p->n_rule) reachwalk(p->n_rule);
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}
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}
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STATIC
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reachwalk(p) register p_gram p; {
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/*
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* Walk through rule p, looking for nonterminals.
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* The nonterminals found are entered as reachable
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*/
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for (;;) {
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switch(g_gettype(p)) {
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case ALTERNATION :
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reachwalk(g_getlink(p)->l_rule);
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break;
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case TERM :
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reachwalk(g_getterm(p)->t_rule);
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break;
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case NONTERM :
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reachable(&nonterms[g_getcont(p)]);
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break;
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case EORULE :
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return;
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}
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p++;
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}
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}
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