From 24c15f34cc263765b77820d9bb3662ed39f70a93 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Sun, 16 Jun 2013 22:23:35 +0200
Subject: [PATCH] augment grammar to ensure start symbol never occurs on rhs
---
src/backends/lalr.c | 33 ++++++++++++++++++++++++---------
1 file changed, 24 insertions(+), 9 deletions(-)
diff --git a/src/backends/lalr.c b/src/backends/lalr.c
index e0414897..bcb1a028 100644
--- a/src/backends/lalr.c
+++ b/src/backends/lalr.c
@@ -2,6 +2,7 @@
#include "../internal.h"
#include "../cfgrammar.h"
#include "../parsers/parser_internal.h"
+#include "contextfree.h"
@@ -274,8 +275,6 @@ HLRDFA *h_lr0_dfa(HCFGrammar *g)
// assigned index.
HSlist *work = h_slist_new(arena);
- // XXX augment grammar?!
-
// make initial state (kernel)
HLRState *start = h_lrstate_new(arena);
assert(g->start->type == HCF_CHOICE);
@@ -596,14 +595,33 @@ bool match_production(HLREnhGrammar *eg, HCFChoice **p,
&& state == endstate);
}
+// desugar parser with a fresh start symbol
+// this guarantees that the start symbol will not occur in any productions
+static HCFChoice *augment(HAllocator *mm__, HParser *parser)
+{
+ HCFChoice *augmented = h_new(HCFChoice, 1);
+
+ HCFStack *stk__ = h_cfstack_new(mm__);
+ stk__->prealloc = augmented;
+ HCFS_BEGIN_CHOICE() {
+ HCFS_BEGIN_SEQ() {
+ HCFS_DESUGAR(parser);
+ } HCFS_END_SEQ();
+ HCFS_THIS_CHOICE->reshape = h_act_first;
+ } HCFS_END_CHOICE();
+ h_cfstack_free(mm__, stk__);
+
+ return augmented;
+}
+
int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params)
{
- // generate CFG from parser
+ // generate (augmented) CFG from parser
// construct LR(0) DFA
// build LR(0) table
// if necessary, resolve conflicts "by conversion to SLR"
- HCFGrammar *g = h_cfgrammar(mm__, parser);
+ HCFGrammar *g = h_cfgrammar_(mm__, augment(mm__, parser));
if(g == NULL) // backend not suitable (language not context-free)
return -1;
@@ -981,21 +999,18 @@ HParserBackendVTable h__lalr_backend_vtable = {
int test_lalr(void)
{
/*
- S -> E
E -> E '-' T
| T
T -> '(' E ')'
| 'n' -- also try [0-9] for the charset paths
*/
-#if 0
HParser *n = h_ch('n');
HParser *E = h_indirect();
HParser *T = h_choice(h_sequence(h_ch('('), E, h_ch(')'), NULL), n, NULL);
HParser *E_ = h_choice(h_sequence(E, h_ch('-'), T, NULL), T, NULL);
h_bind_indirect(E, E_);
-#endif
- HParser *p = h_whitespace(h_ch('n')); //h_sequence(E, NULL);
+ HParser *p = E;
printf("\n==== G R A M M A R ====\n");
HCFGrammar *g = h_cfgrammar(&system_allocator, p);
@@ -1028,7 +1043,7 @@ int test_lalr(void)
h_pprint_lrtable(stdout, g, (HLRTable *)p->backend_data, 0);
printf("\n==== P A R S E R E S U L T ====\n");
- HParseResult *res = h_parse(p, (uint8_t *)" n-(n-((n)))-n", 13);
+ HParseResult *res = h_parse(p, (uint8_t *)"n-(n-((n)))-n", 13);
if(res)
h_pprint(stdout, res->ast, 0, 2);
else
--
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