sS nlLogic_render(IfThen rule) {
  if (rule == null) null;
  ret nlLogic_render(rule.in) + " => " + nlLogic_render(rule.out);
}

sS nlLogic_render(Exp e) {
  if (e cast Func)
    ret e.name + "(" + nlLogic_render(e.arg) + ")";
  if (e cast Sentence)
    ret join(e.tok);
  ret "TODO";
}

srecord IfThen(Exp in, Exp out) {}
sclass Exp {}
srecord Func(S name, Exp arg) extends Exp {}
srecord And(Exp a, Exp b) extends Exp {}
srecord Sentence(L<S> tok) extends Exp {}
srecord Eq(Exp left, Exp right) extends Exp {}