TWHILE
case TWHILE:
while ((execute(t->left, XERROK) == 0) == (t->type == TWHILE))
t = newtp((c == WHILE) ? TWHILE : TUNTIL);
case TWHILE:
(t->type==TWHILE) ? "while" : "until",
case TWHILE:
n1->type = (lasttoken == TWHILE)? NWHILE : NUNTIL;