Function isheadfail

other_src/lua/src/lpeg.cpp:936–942

** A 'headfail' pattern is a pattern that can only fails in its first ** instruction, which must be a check. */

** instruction, which must be a check.
*/
static int isheadfail (Instruction *p) {
  if (!ischeck(p)) return 0;
  /* check that other operations cannot fail */
  for (p += sizei(p); p->i.code != IEnd; p += sizei(p))
    if (!isnofail(p)) return 0;
  return 1;
}


#define checkpattern(L, idx) ((Instruction *)luaL_checkudata(L, idx, PATTERN_T))