/* file name calc4.y */

/*  Calculator with variable identifiers */
/*  Bison specification */

%{
#include <math.h>        /* for pow() function       */
#include "symtab4.h"
%}

%union {
    double  val;       /* values of expressions     */
    symrec  *tptr;     /* symbol table pointer for variables */
    }

%token <val>  NUM
%token <tptr> VAR
%type  <val>  expr

%left '-' '+'
%left '*' '/'
%nonassoc UMINUS
%right '^'

%%

input
    :  /* empty */
    |  input line
    ;

line
    : '\n'
    | VAR '=' expr  '\n'    { $1->value = $3; }
    | expr '\n'             { printf ("\t= %.2f\n", $1); }
    | error '\n'            { yyerrok; }
    ;

expr
    : expr '+' expr          { $$ = $1 + $3; }
    | expr '-' expr          { $$ = $1 - $3; }
    | expr '*' expr          { $$ = $1 * $3; }
    | expr '/' expr          { if ($3 == 0.0)
                                   yyerror("divide by zero");
                               else
                                   $$ = $1 / $3; }
    | '-' expr %prec UMINUS  { $$ = - $2; }
    | expr '^' expr          { $$ = pow($1,$3); }
    | '(' expr ')'           { $$ = $2; }
    |  NUM                   { $$ = $1; } 
    |  VAR                   { $$ = $1->value; }
    ;

%%

symrec *sym_table = (symrec *)0;

main ()
{
  yyparse ();
}

yyerror (char *s)  /* Called by yyparse on error */
{
  printf ("\terror: %s\n", s);
}