hmatch
hmatch(infop, src->u.arrow.rhs, dst);
hmatch(infop, src, dst);
hmatch(infop, nextnp, NULL);
hmatch(infop, np->u.expr.left, nextnp);
hmatch(infop, np->u.expr.right, nextnp);
static void hmatch(struct info *infop, struct node *np, struct node *nextnp);