pantry/projects/gnu.org/bison/test.y

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%{ #include <iostream>
using namespace std;
extern void yyerror (char *s);
extern int yylex ();
%}
%start prog
%%
prog: // empty
| prog expr '\n' { cout << "pass"; exit(0); }
;
expr: '(' ')'
| '(' expr ')'
| expr expr
;
%%
char c;
void yyerror (char *s) { cout << "fail"; exit(0); }
int yylex () { cin.get(c); return c; }
int main() { yyparse(); }