calc.y revision 1.1.1.1 
1/*	$NetBSD: calc.y,v 1.1.1.1 2009/10/29 00:46:53 christos Exp $	*/
2
3%{
4# include <stdio.h>
5# include <ctype.h>
6
7int regs[26];
8int base;
9
10%}
11
12%start list
13
14%token DIGIT LETTER
15
16%left '|'
17%left '&'
18%left '+' '-'
19%left '*' '/' '%'
20%left UMINUS   /* supplies precedence for unary minus */
21
22%% /* beginning of rules section */
23
24list  :  /* empty */
25      |  list stat '\n'
26      |  list error '\n'
27            {  yyerrok ; }
28      ;
29
30stat  :  expr
31            {  printf("%d\n",$1);}
32      |  LETTER '=' expr
33            {  regs[$1] = $3; }
34      ;
35
36expr  :  '(' expr ')'
37            {  $$ = $2; }
38      |  expr '+' expr
39            {  $$ = $1 + $3; }
40      |  expr '-' expr
41            {  $$ = $1 - $3; }
42      |  expr '*' expr
43            {  $$ = $1 * $3; }
44      |  expr '/' expr
45            {  $$ = $1 / $3; }
46      |  expr '%' expr
47            {  $$ = $1 % $3; }
48      |  expr '&' expr
49            {  $$ = $1 & $3; }
50      |  expr '|' expr
51            {  $$ = $1 | $3; }
52      |  '-' expr %prec UMINUS
53            {  $$ = - $2; }
54      |  LETTER
55            {  $$ = regs[$1]; }
56      |  number
57      ;
58
59number:  DIGIT
60         {  $$ = $1; base = ($1==0) ? 8 : 10; }
61      |  number DIGIT
62         {  $$ = base * $1 + $2; }
63      ;
64
65%% /* start of programs */
66
67main ()
68
69{
70    while(!feof(stdin)) {
71      yyparse();
72   }
73}
74
75yyerror(char *s)
76{
77   fprintf(stderr, "%s\n", s);
78}
79
80
81yylex() {   /* lexical analysis routine */
82            /* returns LETTER for a lower case letter, yylval = 0 through 25 */
83            /* return DIGIT for a digit, yylval = 0 through 9 */
84            /* all other characters are returned immediately */
85
86      int c;
87
88      while( (c=getchar()) == ' ' )   { /* skip blanks */ }
89
90      /* c is now nonblank */
91
92      if( islower( c )) {
93         yylval = c - 'a';
94         return ( LETTER );
95         }
96      if( isdigit( c )) {
97         yylval = c - '0';
98         return ( DIGIT );
99         }
100      return( c );
101      }
102