src/calc.y

   1 %{
   2 #include <stdio.h>  /* for printf() */
   3 #include <stdlib.h>  /* for strtod() */
   4 #include <ctype.h>
   5 #include <math.h>  /* for pow() */
   6
   7 #define YYSTYPE double
   8
   9 int yylex(void);
  10 void yyerror(const char *);
  11
  12 YYSTYPE yyreturn;
  13 %}
  14
  15 %token NUM
  16 %left '-' '+'
  17 %left '*' '/'
  18 %left NEG      /* negation: unary minus */
  19 %right '^'     /* exponentation */
  20
  21 %%
  22
  23 line: exp                { yyreturn = $1; }
  24 ;
  25
  26 exp: NUM                 { $$ = $1; }
  27     | exp '+' exp        { $$ = $1 + $3; }
  28     | exp '-' exp        { $$ = $1 - $3; }
  29     | exp '*' exp        { $$ = $1 * $3; }
  30     | exp '/' exp        { $$ = $1 / $3; }
  31     | '-' exp %prec NEG  { $$ = -$2; }
  32     | exp '^' exp        { $$ = pow($1, $3); }
  33     | '(' exp ')'        { $$ = $2; }
  34 ;
  35
  36 %%
  37
  38 /*#define EXPRESSION_VERBOSE*/
  39
  40 static const char *yydata;
  41
  42 int parse_expression(const char *data, double *d) {
  43     int r;
  44
  45 #ifdef EXPRESSION_VERBOSE
  46     printf("%s = ", data);
  47 #endif
  48
  49     if(!data) {
  50 #ifdef EXPRESSION_VERBOSE
  51         printf(" [NULL]\n");
  52 #endif
  53         return 1;
  54     }
  55
  56     yydata = data;
  57     r = yyparse();
  58
  59     *d = yyreturn;
  60 #ifdef EXPRESSION_VERBOSE
  61     printf("%f\n", yyreturn);
  62 #endif
  63
  64     return r;
  65 }
  66
  67 int yylex(void) {
  68     char *p;
  69
  70     while(isspace(*yydata)) yydata ++;
  71
  72     if(!*yydata) return 0;
  73
  74     if(isdigit(*yydata) || *yydata == '.') {
  75         yylval = strtod(yydata, &p);
  76         if(p == yydata) return 0;
  77         yydata = p;
  78
  79         while(isspace(*yydata)) yydata ++;
  80
  81         return NUM;
  82     }
  83
  84     return *yydata++;
  85 }
  86
  87 void yyerror(const char *s) {
  88     fprintf(stderr, "%s: \"%s\"\n", s, yydata);
  89 }