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yacc.c: isolate yyexpected_tokens

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Provide users with a means to query for the currently allowed tokens.
Could be used for autocompletion for instance.

* data/skeletons/yacc.c (yyexpected_tokens): New, extracted from
yysyntax_error_arguments.
* examples/c/calc/calc.y (PRINT_EXPECTED_TOKENS): New.
Use it.
This commit is contained in:
Akim Demaille
2020-01-06 20:04:58 +01:00
parent ee97f37cb4
commit 8637438cee
2 changed files with 92 additions and 43 deletions
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32
examples/c/calc/calc.y
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@@ -1,15 +1,35 @@
%code top {
#include <ctype.h> /* isdigit. */
#include <stdbool.h>
#include <stdio.h> /* For printf, etc. */
#include <string.h> /* strcmp. */
int yylex (void);
void yyerror (char const *);
bool show_expected = false;
#define PRINT_EXPECTED_TOKENS() \
do { \
if (show_expected) \
{ \
yyparse_context_t ctx \
= {yyssp, yytoken, yyesa, &yyes, &yyes_capacity}; \
int tokens[YYNTOKENS]; \
int cnt = yyexpected_tokens (&ctx, tokens, YYNTOKENS); \
fprintf (stderr, "expected tokens in state %d rule %d (%d):", \
*yyssp, yyn - 1, cnt); \
for (int i = 0; i < cnt; ++i) \
fprintf (stderr, " %s", yysymbol_name(tokens[i])); \
fprintf (stderr, "\n"); \
} \
} while (0)
}
%define api.header.include {"calc.h"}
%define api.value.type union /* Generate YYSTYPE from these types: */
%define parse.error custom
%define parse.lac full
%token <double> NUM "number"
%type <double> expr term fact
@@ -23,8 +43,8 @@
%% /* The grammar follows. */
input:
%empty
| input line
%empty { PRINT_EXPECTED_TOKENS (); }
| input line { PRINT_EXPECTED_TOKENS (); }
;
line:
@@ -46,8 +66,8 @@ term:
;
fact:
"number"
| '(' expr ')' { $$ = $2; }
"number" { PRINT_EXPECTED_TOKENS (); }
| '(' expr { PRINT_EXPECTED_TOKENS (); } ')' { $$ = $expr; }
;
%%
@@ -110,7 +130,9 @@ main (int argc, char const* argv[])
{
/* Enable parse traces on option -p. */
for (int i = 1; i < argc; ++i)
if (!strcmp (argv[i], "-p"))
if (!strcmp (argv[i], "-e"))
show_expected = 1;
else if (!strcmp (argv[i], "-p"))
yydebug = 1;
return yyparse ();
}