Design LALR Bottom up Parser using YACC.

Design LALR Bottom up Parser.

<parser.l>

%{

#include<stdio.h> #include "y.tab.h"

%}

%%

[0-9]+ {yylval.dval=atof(yytext); return DIGIT;

}

\n|. return yytext[0];

%%

<parser.y>

%{

/*This YACC specification file generates the LALR parser for the program considered in experiment 4.*/

#include<stdio.h>

%}

%union

{

double dval;

}

%token <dval> DIGIT

%type <dval> expr

%type <dval> term

%type <dval> factor

%%

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

}

;

expr: expr '+' term {$$=$1 + $3 ;}

| term

;

term: term '*' factor {$$=$1 * $3 ;}

| factor

;

factor: '(' expr ')' {$$=$2 ;}

| DIGIT

 

;

%%

int main()

{

yyparse();

}

yyerror(char *s)

{

printf("%s",s);

}

Output:

$lex parser.l

$yacc –d parser.y

$cc lex.yy.c y.tab.c –ll –lm

$./a.out 2+3

5.0000

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