Книга: UNIX — универсальная среда программирования

3.1.2 hoc.y

3.1.2 hoc.y
%{
#define YYSTYPE double /* data type of yacc stack */
%}
%token NUMBER
%left '+' /* left associative, same precedence */
%left '*' '/' /* left assoc., higher precedence */
%%
list : /* nothing */
 | list 'n'
 | list expr 'n' { printf("t%.8gn", $2); }
 ;
expr: NUMBER { $$ = $1; }
 | expr '+' expr { $$ = $1 + $3; }
 | expr '-' expr { $$ = $1 - $3; }
 | expr '*' expr { $$ = $1 * $3; }
 | expr '/' expr { $$ = $1 / $3; }
 | '(' expr ')' { $$ = $2; }
 ;
%%
/* end of grammar */
#include <stdio.h>
#include <ctype.h>
char *progname; /* for error messages */
int lineno = 1;
main(argc, argv) /* hoc1 */
 char *argv[];
{
 progname = argv[0];
 yyparse();
}
yylex() /* hoc1 */
{
 int c;
 while ((c=getchar()) == ' ' || c == 't')
  ;
 if (c == EOF)
  return 0;
 if (c == '.' || isdigit(c)) { /* number */
  ungetc(c, stdin);
 scanf("%lf", &yylval);
 return NUMBER;
 if (c == 'n')
  lineno++;
 return c;
}
yyerror(s) /* called for yacc syntax error */
 char *s;
{
 warning(s, (char*)0);
}
warning(s, t) /* print warning message */
 char *s, *t;
{
 fprintf(stderr, "%s: %s", progname, s);
 if (t)
  fprintf(stderr, " %s", t);
 fprintf(stderr, " near line %dn", lineno);
}

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