I'm trying to convert a calculator from Bison to Lemon.
I ran into an unexpected problem involving standard input where
the two programs behave quite differently. The Bison version
prints the result immediately after pressing [Enter]. With the
Lemon version, the result is delayed until I type a new
expression and press [Enter].
I've created tiny Bison and Lemon grammars and Flex scanners to
illustrate the problem. This is on Windows 7, using a July 2014
version of Lemon, Bison 2.41, and gcc (tdm64-2) 4.8.1.
*A simple session with the Bison version*
3 + 4[enter]
7
6 + 2[enter]
8
*Notice how the result is returned after pressing [Enter] after
the simple expression.*
*A simple session with the Lemon version*
3 + 4[enter]
6 + 2[enter]
7
1 + 1[enter]
8
^Z
2
*Notice how the result is only returned after the entering of a
second expression and pressing of [Enter] (ctrl Z signals
end-of-input for cmd.exe).*
What have I done wrong?
Bison/Flex version source
=========================
badd.l:
%{
#include "y.tab.h"
#include <stdlib.h>
%}
%%
[0-9]+ {yylval = atoi(yytext); return INTEGER;}
[+] return PLUS;
[\n] return NL;
[ \t] ; /* skip whitespace */
. {printf("Unknown character '%c'\n", yytext[0]); return 0;}
%%
int yywrap(void) {
return 1;
}
badd.y:
%{
#include <stdio.h>
int yylex(void);
void yyerror(char *);
%}
%token INTEGER PLUS NL
%left PLUS MINUS
%%
prog: prog expr NL { printf("%d\n", $2); }
|
;
expr: INTEGER { $$ = $1; }
| expr PLUS expr { $$ = $1 + $3; }
;
%%
void yyerror(char *s) {
fprintf(stderr, "%s\n", s);
}
int main(void) {
yyparse();
return 0;
}
To build:
bison -y -d badd.y
flex badd.l
gcc y.tab.c lex.yy.c -o badd.exe
Lemon/Flex version source
=========================
ladd.l
%{
#include "ladd.h"
#include <stdlib.h>
extern int yylval;
%}
%%
[0-9]+ {yylval = atoi(yytext); return INTEGER;}
[+] return PLUS;
[\n] return NL;
[ \t] ; /* skip whitespace */
. {printf("Unknown character '%c'\n", yytext[0]); return 0;}
%%
int yywrap(void) {
return 1;
}
ladd.y:
%include { #include <assert.h> }
%syntax_error { printf("Lemon syntax error\n"); }
%token_type {int}
%left PLUS MINUS .
start ::= prog .
prog ::= prog expr(a) NL . { printf("%d\n", a); }
prog ::= .
expr(a) ::= INTEGER(b) . { a = b; }
expr(a) ::= expr(b) PLUS expr(c) . { a = b + c; }
main.c:
<!-- language: lang-c -->
#include <stdio.h>
#include <stdlib.h>
void *ParseAlloc(void *(*mallocProc)(size_t));
void ParseFree(void *p, void (*freeProc)(void*));
void Parse(void *yyp, int yymajor, int foo);
int yylex(void);
int yylval;
int main(void) {
void *pParser;
int tok;
pParser = ParseAlloc(malloc);
while ((tok = yylex()) != 0) {
Parse(pParser, tok, yylval);
}
Parse(pParser, 0, 0);
ParseFree(pParser, free );
return 0;
}
To build:
lemon ladd.y
flex ladd.l
gcc main.c ladd.c lex.yy.c -o ladd.exe
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