mycalc.y

%{
#include <stdio.h>
#include <stdlib.h>
#define YYDEBUG 1
%}
%union{
    int      int_value;
    double   double_value;
}
%token <double_value>    DOUBLE_LITERAL
%token ADD SUB MUL DIV CR
%type <double_value> expression term primary_expression
%%
line_list
    : line
    | line_list line
    ;
line
    : expression CR
    {
        printf(">>%lf\n",$1);
    }
expression
    : term
    | expression ADD term
    {
        $$ = $1 + $3;
    }
    | expression SUB term
    {
        $$ = $1 - $3;
    }
    ;
term
    : primary_expression
    | term MUL primary_expression
    {
        $$ = $1 * $3;
    }
    | term DIV primary_expression
    {
        $$ = $1 / $3;
    }
    ;
primary_expression
    : DOUBLE_LITERAL
    ;
%%
int
yyerror(char const *str)
{
    extern char *yytext;
    fprintf(stderr, "parser error near %s\n", yytext);
    return 0;
}

int main(void)
{
    extern int yyparse(void);
    extern FILE *yyin;

    yyin = stdin;
    if(yyparse()){
        fprintf(stderr, "Error ! Error ! Error!\n");
        exit(1);
    }
}