101 lines
1.8 KiB
Plaintext
101 lines
1.8 KiB
Plaintext
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%code top {
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#include <assert.h>
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#include <ctype.h> /* isdigit. */
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#include <stdio.h> /* printf. */
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#include <stdlib.h> /* abort. */
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#include <string.h> /* strcmp. */
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int yylex (void);
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void yyerror (char const *);
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}
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/* Generate YYSTYPE from the types used in %token and %type. */
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%define api.value.type union
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%token <double> NUM "number"
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%type <double> expr term fact
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/* Generate the parser description file (calc.output). */
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%verbose
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/* Nice error messages with details. */
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%define parse.error verbose
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/* Enable run-time traces (yydebug). */
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%define parse.trace
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/* Formatting semantic values in debug traces. */
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%printer { fprintf (yyo, "%g", $$); } <double>;
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%% /* The grammar follows. */
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input:
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%empty
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| input line
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;
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line:
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'\n'
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| expr '\n' { printf ("%.10g\n", $1); }
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| error '\n' { yyerrok; }
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;
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expr:
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expr '+' term { $$ = $1 + $3; }
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| expr '-' term { $$ = $1 - $3; }
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| term
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;
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term:
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term '*' fact { $$ = $1 * $3; }
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| term '/' fact { $$ = $1 / $3; }
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| fact
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;
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fact:
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"number"
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| '(' expr ')' { $$ = $2; }
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;
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%%
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int
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yylex (void)
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{
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int c;
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/* Ignore white space, get first nonwhite character. */
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while ((c = getchar ()) == ' ' || c == '\t')
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continue;
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if (c == EOF)
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return 0;
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/* Char starts a number => parse the number. */
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if (c == '.' || isdigit (c))
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{
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ungetc (c, stdin);
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if (scanf ("%lf", &yylval.NUM) != 1)
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abort ();
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return NUM;
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}
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/* Any other character is a token by itself. */
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return c;
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}
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/* Called by yyparse on error. */
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void
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yyerror (char const *s)
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{
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fprintf (stderr, "%s\n", s);
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}
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int
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main (int argc, char const* argv[])
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{
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/* Enable parse traces on option -p. */
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for (int i = 1; i < argc; ++i)
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if (!strcmp (argv[i], "-p"))
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yydebug = 1;
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return yyparse ();
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}
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