/* http://www.gnu.org/software/bison/manual/html_mono/bison.html.gz */
/* Infix notation calculator. */
%{
#define YYSTYPE double
#include
#include
#include
#include
int yylex (void);
void yyerror (char const *);
char * cursor = "#";
%}
/* Bison declarations. */
%token NUM
%left '-' '+'
%left '*' '/'
%left NEG /* negation--unary minus */
%right '^' /* exponentiation */
%% /* Grammar rules and actions follow. */
input: /* empty */
| input line
;
line: '\n' { printf ("\n%s ", cursor); }
| exp '\n' { printf ("\t%.10g\n%s ", $1, cursor); }
| error '\n' { yyerrok; }
;
exp: NUM { $$ = $1; }
| exp '+' exp { $$ = $1 + $3; }
| exp '-' exp { $$ = $1 - $3; }
| exp '*' exp { $$ = $1 * $3; }
| exp '/' exp { $$ = $1 / $3; }
| '-' exp %prec NEG { $$ = -$2; }
| exp '^' exp { $$ = pow ($1, $3); }
| '(' exp ')' { $$ = $2; }
;
%%
/* The lexical analyzer returns a double floating point
number on the stack and the token NUM, or the numeric code
of the character read if not a number. It skips all blanks
and tabs, and returns 0 for end-of-input. */
#include
int
yylex (void)
{
int c;
/* Skip white space. */
while ((c = getchar ()) == ' ' || c == '\t')
;
/* Process numbers. */
if (c == '.' || isdigit (c))
{
ungetc (c, stdin);
//ungetc (c);
scanf ("%lf", &yylval);
return NUM;
}
/* Return end-of-input. */
if (c == EOF)
return 0;
/* Return a single char. */
return c;
}
int
main (void)
{
printf("%s ", cursor);
return yyparse ();
}
#include
/* Called by yyparse on error. */
void
yyerror (char const *s)
{
fprintf (stderr, "%s\n%s", s, cursor);
}