%{
#include <ctype.h>
#include <stdio.h>
#define YYSTYPE double /* defines type for yylval, int by default */
%}

%token NUMBER

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

lines : lines expr '\n' {printf("%g\n", $2);} /* %g shorter of scientific/fixed notation */
      | lines '\n'
      | /* empty */
      ;
expr  :  expr '+' expr {$$ = $1 + $3;}  /* $$ is attribute value of LHS */
      |  expr '-' expr {$$ = $1 - $3;} 
      |  expr '*' expr {$$ = $1 * $3;} 
      |  expr '/' expr {$$ = $1 / $3;} 
      |  '(' expr ')' {$$ = $2;} 
      | '-' expr %prec UMINUS {$$ = -$2;}
      | NUMBER  
      ;
%%
yylex( )
{
int c;
while ((c = getchar( ) ) == ' ')   
      ;
if ((c == '.' || isdigit(c)))
{
   ungetc(c, stdin);
   scanf("%lf", &yylval);
   return NUMBER;
}
return c;
}