%{
#include <stdio.h>
#include <math.h>

int regs[26];

  %}

%start list

%token DIGIT LETTER

%left '|'
%left '&'
%left '+' '-'
%left '*' '/' '%'
%left UMINUS  /*supplies precedence for unary minus */

%%                   /* beginning of rules section */

list:                       /*empty */
         |
        list stat '\n'
         |
        list error '\n'
{
  yyerrok;
}
;

stat:    expr
{
  printf("%d\n",$1);
}
         |
         LETTER '=' expr
{
  regs[$1] = $3;
}

;

expr:    '(' expr ')'
{
  $$ = $2;
}
         |
         expr '*' expr
{

  $$ = $1 * $3;
}
         |
         expr '/' expr
{
  $$ = $1 / $3;
}
         |
         expr '%' expr
{
  $$ = $1 % $3;
}
         |
         expr '+' expr
{
  $$ = $1 + $3;
}
         |
         expr '-' expr
{
  $$ = $1 - $3;
}
         |
         expr '&' expr
{
  $$ = $1 & $3;
}
         |
         expr '|' expr
{
  $$ = $1 | $3;
}
         |

        '-' expr %prec UMINUS
{
  $$ = -$2;
}
         |
         LETTER
{
  $$ = regs[$1];
}

         |
         number
         ;

number:  DIGIT
{
  $$ = $1;
}       |
         number DIGIT
{
  $$ = 10 * $1 + $2;
}
;

%%
main()
{
  return(yyparse());
}

yyerror(s)
     char *s;
{
  fprintf(stderr, "%s\n",s);
}

yywrap()
{
  return(1);
}