calc.y revision 1.1.1.7 
1/*	$NetBSD: calc.y,v 1.1.1.7 2016/01/09 21:59:45 christos Exp $	*/
2
3%{
4# include <stdio.h>
5# include <ctype.h>
6
7int regs[26];
8int base;
9
10extern int yylex(void);
11static void yyerror(const char *s);
12
13%}
14
15%start list
16
17%token DIGIT LETTER
18
19%left '|'
20%left '&'
21%left '+' '-'
22%left '*' '/' '%'
23%left UMINUS   /* supplies precedence for unary minus */
24
25%% /* beginning of rules section */
26
27list  :  /* empty */
28      |  list stat '\n'
29      |  list error '\n'
30            {  yyerrok ; }
31      ;
32
33stat  :  expr
34            {  printf("%d\n",$1);}
35      |  LETTER '=' expr
36            {  regs[$1] = $3; }
37      ;
38
39expr  :  '(' expr ')'
40            {  $$ = $2; }
41      |  expr '+' expr
42            {  $$ = $1 + $3; }
43      |  expr '-' expr
44            {  $$ = $1 - $3; }
45      |  expr '*' expr
46            {  $$ = $1 * $3; }
47      |  expr '/' expr
48            {  $$ = $1 / $3; }
49      |  expr '%' expr
50            {  $$ = $1 % $3; }
51      |  expr '&' expr
52            {  $$ = $1 & $3; }
53      |  expr '|' expr
54            {  $$ = $1 | $3; }
55      |  '-' expr %prec UMINUS
56            {  $$ = - $2; }
57      |  LETTER
58            {  $$ = regs[$1]; }
59      |  number
60      ;
61
62number:  DIGIT
63         {  $$ = $1; base = ($1==0) ? 8 : 10; }
64      |  number DIGIT
65         {  $$ = base * $1 + $2; }
66      ;
67
68%% /* start of programs */
69
70int
71main (void)
72{
73    while(!feof(stdin)) {
74	yyparse();
75    }
76    return 0;
77}
78
79static void
80yyerror(const char *s)
81{
82    fprintf(stderr, "%s\n", s);
83}
84
85int
86yylex(void)
87{
88	/* lexical analysis routine */
89	/* returns LETTER for a lower case letter, yylval = 0 through 25 */
90	/* return DIGIT for a digit, yylval = 0 through 9 */
91	/* all other characters are returned immediately */
92
93    int c;
94
95    while( (c=getchar()) == ' ' )   { /* skip blanks */ }
96
97    /* c is now nonblank */
98
99    if( islower( c )) {
100	yylval = c - 'a';
101	return ( LETTER );
102    }
103    if( isdigit( c )) {
104	yylval = c - '0';
105	return ( DIGIT );
106    }
107    return( c );
108}
109