1%code          { /* CODE-DEFAULT2 */ }
2%code          { /* CODE-DEFAULT */ }
3%code requires { /* CODE-REQUIRES */ }
4%code provides { /* CODE-PROVIDES */ }
5%code top      { /* CODE-TOP */ }
6%code provides { /* CODE-PROVIDES2 */ }
7
8%{
9# include <stdio.h>
10# include <ctype.h>
11
12int regs[26];
13int base;
14
15extern int yylex(void);
16static void yyerror(const char *s);
17
18%}
19
20%start list
21
22%token DIGIT LETTER
23
24%left '|'
25%left '&'
26%left '+' '-'
27%left '*' '/' '%'
28%left UMINUS   /* supplies precedence for unary minus */
29
30%% /* beginning of rules section */
31
32list  :  /* empty */
33      |  list stat '\n'
34      |  list error '\n'
35            {  yyerrok ; }
36      ;
37
38stat  :  expr
39            {  printf("%d\n",$1);}
40      |  LETTER '=' expr
41            {  regs[$1] = $3; }
42      ;
43
44expr  :  '(' expr ')'
45            {  $$ = $2; }
46      |  expr '+' expr
47            {  $$ = $1 + $3; }
48      |  expr '-' expr
49            {  $$ = $1 - $3; }
50      |  expr '*' expr
51            {  $$ = $1 * $3; }
52      |  expr '/' expr
53            {  $$ = $1 / $3; }
54      |  expr '%' expr
55            {  $$ = $1 % $3; }
56      |  expr '&' expr
57            {  $$ = $1 & $3; }
58      |  expr '|' expr
59            {  $$ = $1 | $3; }
60      |  '-' expr %prec UMINUS
61            {  $$ = - $2; }
62      |  LETTER
63            {  $$ = regs[$1]; }
64      |  number
65      ;
66
67number:  DIGIT
68         {  $$ = $1; base = ($1==0) ? 8 : 10; }
69      |  number DIGIT
70         {  $$ = base * $1 + $2; }
71      ;
72
73%% /* start of programs */
74
75int
76main (void)
77{
78    while(!feof(stdin)) {
79	yyparse();
80    }
81    return 0;
82}
83
84static void
85yyerror(const char *s)
86{
87    fprintf(stderr, "%s\n", s);
88}
89
90int
91yylex(void)
92{
93	/* lexical analysis routine */
94	/* returns LETTER for a lower case letter, yylval = 0 through 25 */
95	/* return DIGIT for a digit, yylval = 0 through 9 */
96	/* all other characters are returned immediately */
97
98    int c;
99
100    while( (c=getchar()) == ' ' )   { /* skip blanks */ }
101
102    /* c is now nonblank */
103
104    if( islower( c )) {
105	yylval = c - 'a';
106	return ( LETTER );
107    }
108    if( isdigit( c )) {
109	yylval = c - '0';
110	return ( DIGIT );
111    }
112    return( c );
113}
114