%pure-parser

%parse-param { int regs[26] 
%parse-param { int *base 

%lex-param { int *base 

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

#ifdef YYBISON
#define YYSTYPE int
#define YYLEX_PARAM base
#define YYLEX_DECL() yylex(YYSTYPE *yylval, int *YYLEX_PARAM)
#define YYERROR_DECL() yyerror(int regs[26], int *base, const char *s)
int YYLEX_DECL();
static void YYERROR_DECL();
#endif

%}

%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
         {  $$ = $1; (*base) = ($1==0) ? 8 : 10; }
      |  number DIGIT
         {  $$ = (*base) * $1 + $2; }
      ;

%% /* start of programs */

#ifdef YYBYACC
extern int YYLEX_DECL();
#endif

int
main (void)
{
    int regs[26];
    int base = 10;

    while(!feof(stdin)) {
	yyparse(regs, &base);
    }
    return 0;
}

#define UNUSED(x) ((void)(x))

static void
YYERROR_DECL()
{
    UNUSED(regs); /* %parse-param regs is not actually used here */
    UNUSED(base); /* %parse-param base is not actually used here */
    fprintf(stderr, "%s\n", s);
}

int
YYLEX_DECL()
{
	/* lexical analysis routine */
	/* returns LETTER for a lower case letter, yylval = 0 through 25 */
	/* return DIGIT for a digit, yylval = 0 through 9 */
	/* all other characters are returned immediately */

    int c;

    while( (c=getchar()) == ' ' )   { /* skip blanks */ }

    /* c is now nonblank */

    if( islower( c )) {
	*yylval = (c - 'a');
	return ( LETTER );
    }
    if( isdigit( c )) {
	*yylval = (c - '0') % (*base);
	return ( DIGIT );
    }
    return( c );
}
