Unintentional concatenation in Bison/Yacc grammar.
- by troutwine
I am experimenting with lex and yacc and have run into a strange issue, but I think it would be best to show you my code before detailing the issue. This is my lexer:
%{
#include <stdlib.h>
#include <string.h>
#include "y.tab.h"
void yyerror(char *);
%}
%%
[a-zA-Z]+ {
yylval.strV = yytext;
return ID;
}
[0-9]+ {
yylval.intV = atoi(yytext);
return INTEGER;
}
[\n] { return *yytext; }
[ \t] ;
. yyerror("invalid character");
%%
int yywrap(void) {
return 1;
}
This is my parser:
%{
#include <stdio.h>
int yydebug=1;
void prompt();
void yyerror(char *);
int yylex(void);
%}
%union {
int intV;
char *strV;
}
%token INTEGER ID
%%
program: program statement EOF { prompt(); }
| program EOF { prompt(); }
| { prompt(); }
;
args: /* empty */
| args ID { printf(":%s ", $<strV>2); }
;
statement: ID args { printf("%s", $<strV>1); }
| INTEGER { printf("%d", $<intV>1); }
;
EOF: '\n'
%%
void yyerror(char *s) {
fprintf(stderr, "%s\n", s);
}
void prompt() {
printf("> ");
}
int main(void) {
yyparse();
return 0;
}
A very simple language, consisting of no more than strings and integer and a basic REPL. Now, you'll note in the parser that args are output with a leading colon, the intention being that, when combined with the first pattern of the rule of the statement the interaction with the REPL would look something like this:
> aaa aa a
:aa :a aaa>
However, the interaction is this:
> aaa aa a
:aa :a aaa aa aa
>
Why does the token ID in the following rule
statement: ID args { printf("%s", $<strV>1); }
| INTEGER { printf("%d", $<intV>1); }
;
have the semantic value of the total input string, newline included? How can my grammar be reworked so that the interaction I intended?
