srecord IfThen(Exp in, Exp out) {
  S text() { ret in.text() + " => " + out.text(); }
}

abstract sclass Exp { abstract S text(); }

srecord Func(S name, Exp arg) extends Exp {
  S text() {
    ret name + "(" + arg.text() + ")";
  }
}

srecord And(Exp a, Exp b) extends Exp {
  S text() {
    ret a.text() + " && " + b.text();
  }
}

abstract sclass Literal extends Exp { abstract S text(); }
srecord Sentence(L<S> tok) extends Literal { S text() { ret join(tok); } }
srecord Sentence2(S text) extends Literal { S text() { ret text; } }

srecord Eq(Exp left, Exp right) extends Exp {
  S text() {
    ret left.text() + " = " + right.text();
  }