%{
#include <math.h>
%}

%union{
        double dval;
}

%token  <dval> NUMBER 
%token  PLUS    MINUS   TIMES   DIVIDE  POWER
%token  LEFT_PARENTHESIS        RIGHT_PARENTHESIS
%token  END


%left   PLUS    MINUS
%left   TIMES   DIVIDE
%left   NEG
%right  POWER

%type <dval> Expression
%start Input

%%

Input:	Line
	| Input Line
        ;



Line:	END
        | Expression END                { printf("Result: %f\n",$1); }
        ;


Expression:	NUMBER                        { $$=$1; }

        | Expression PLUS Expression    { $$=$1+$3; }
        | Expression MINUS Expression   { $$=$1-$3; }
        | Expression TIMES Expression   { $$=$1*$3; }
        | Expression DIVIDE Expression  { $$=$1/$3; }
        | MINUS Expression %prec NEG    { $$=-$2; }
        | Expression POWER Expression   { $$=pow($1,$3); }
        | LEFT_PARENTHESIS Expression RIGHT_PARENTHESIS { $$=$2; }
        ;

%%
int yyerror(char *s) {
  printf("%s\n",s);
}

int main(void) {
  yyparse();
}