Книга: UNIX — универсальная среда программирования

3.3.3 hoc.y

3.3.3 hoc.y
%{
#include "hoc.h"
extern double Pow();
%}
%union {
 double val; /* actual value */
 Symbol *sym; /* symbol table pointer */
}
%token <val> NUMBER
%token <sym> VAR BLTIN UNDEF
%type <val> expr asgn
%right '=' %left '+' '-'
%left '*' '/'
%left UNARYMINUS
%right /* exponentiation */
%%
list: /* nothing */
 | list 'n'
 | list asgn 'n'
 | list expr 'n' { printf("t%.8gn", $2); }
 | list error 'n' { yyerrok; }
 ;
asgn: VAR '=' expr { $$=$1->u.val=$3; $1->type = VAR; }
 ;
expr: NUMBER
 | VAR { if ($l->type == UNDEF)
  execerror("undefined variable", $1->name);
  $$ = $1->u.val;
 }
 | asgn
 | BLTIN '(' expr ')' { $$ = (*($1->u.ptr))($3); }
 | expr '+' expr { $$ = $1 + $3; }
 | expr '-' expr { $$ = $1 - $3; }
 | expr '*' expr { $$ = $1 * $3; }
 | expr '/' expr {
  if ($3 == 0.0)
  execerror("division by zero", "");
  $$ = $1 / $3;
 }
 | expr '^' expr { $$ = Pow($1, $3); }
 | '(' expr ')' { $$ = $2; }
 | '-' expr %prec UNARYMINUS { $$ = -$2; }
 ;
%%
/* end of grammar */
#include <stdio.h>
#include <ctype.h>
char *progname;
int lineno = 1;
#include <signal.h>
#include <setjmp.h>
jmp_buf begin;
main(argc, argv) /* hoc3 */
 char *argv[];
{
 int fpecatch();
 progname = argv[0];
 init();
 setjmp(begin);
 signal(SIGFPE, fpecatch);
 yyparse();
}
yylex() /* hoc3 */
{
 int c;
 while ((c=getchar()) == ' ' || c == 't')
  ;
 if (c == EOF)
  return 0;
 if (c == '.' || isdigit(c)) {
  /* number */
  ungetc(c, stdin);
  scanf("%lf", &yylval.val);
  return NUMBER;
 }
 if (isalpha(c)) {
  Symbol *s;
  char sbuf[100], *p = sbuf;
  do {
   *p++ = c;
  } while ((c=getchar()) != EOF && isalnum(c));
  ungetc(c, stdin);
  *p = '';
  if ((s=lookup(sbuf)) == 0)
   s = install(sbuf, UNDEF, 0.0);
  yylval.sym = s;
  return s->type == UNDEF ? VAR : s->type;
 }
 if (c == 'n')
  lineno++;
 return c;
}
yyerror(s)
 char *s;
{
 warning(s, (char *)0);
}
execerror(s, t) /* recover from run-time error */
 char *s, *t;
{
 warning(s, t);
 longjmp(begin, 0);
}
fpecatch() /* catch floating point exceptions */
 execerror("floating point exception", (char*)0);
}
warning(s, t)
 char *s, *t;
{
 fprintf(stderr, "%s: %s", progname, s);
 if (t && *t)
  fprintf (stderr, " %s", t);
 fprintf(stderr, " near line %dn", lineno);
}

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