srecord IfThen(Exp in, Exp out) {}
sclass Exp {}
srecord Func(S name, Exp arg) extends Exp {}
srecord And(Exp a, Exp b) extends Exp {}

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 {}