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From: rom@mvsun.ericsson.se (Robert Malmgren TK/DG)
Newsgroups: comp.unix.questions
Subject: Lex & Yacc
Summary: Why doesn't my example work?
Keywords: lex, yacc
Message-ID: <rom.668103436@mvsun>
Date: 4 Mar 91 16:17:16 GMT
Sender: news@ericsson.se
Distribution: comp
Organization: Ericsson
Lines: 49

I'm trying to learn yacc and lex, but I'm having a tough time. I've written
a simple testprogram that does an arithmetic operation on two args. The 
problem is that it works the first time I enter the digits and prints the
correct result, but fails with a 'syntax error'-message the second time. Why? 
Could someone please enlighten me.

--------------------------------------- c.l -----------------------------------
%%
[ \t]+	;

[0-9]+	{
	sscanf(yytext, "%d", &yylval);
	return INTEGER;
	}

[-+\*]	return yytext[0];

\n	return '\n';
%%
--------------------------------------- c.y -----------------------------------
%token INTEGER

%%
line:		'\n'
	|	expr '\n'
			{printf("%d\n", $1);}
	;

expr:  		expr '+' expr 
			{$$ = $1 + $3;}
	|	expr '-' expr
			{$$ = $1 - $3;}
	|	expr '*' expr
			{$$ = $1 * $3;}
	|	int
	;

int:		INTEGER  {
			$$ = $1;
		}
	;
%%
#include "lex.yy.c"


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