*/

%{

   #include <stdio.h>

   #include <ctype.h>

   int regs[26]; 

   int base;

   int yyerror();

   int yylex();

%}

%start list

%token DIGIT LETTER

%left MINUS PLUS MUL DIV

%left UMINUS

%%

list : /* empty */ 

	| list stat '\n' 

	| list error '\n' { yyerrok; };

stat : 

	expr { (void) printf( "RESULT: %d\n", $1 ); } 

	| LETTER '=' expr { regs[$1] = $3; }

	;

   expr      :  '(' expr ')'

             {

                   $$ = $2;

             }

             |  expr PLUS expr

             {

                   $$ = $1 + $3;

             }

             |  expr MINUS expr

             {

                   $$ = $1 - $3;

             }

             |  expr MUL expr

             { 

                   $$ = $1 * $3;

             }

             |  expr DIV expr

             {

                   $$ = $1 / $3;

             }

             |  MINUS expr  %prec UMINUS

             {

                   $$ = -$2;

             }

             |  LETTER

             {

                   $$ = regs[$1];

             }

             |  number

             ;

   number    :   DIGIT

             {

                    $$ = $1; base = ($1==0) ? 8 : 10;

             }

             |   number DIGIT

             {

                    $$ = base * $1 + $2;

             }

             ;

%%

int yyerror() 

{

	printf("ERROR\n");

	return 0;

}

int yywrap() 

{

	return 1;

}