What is magical and mind-bending about `amb` is that it rewinds through arbitrary complicated call stacks, similar to an exception. This is why it's necessarily a special form.
The Haskell version requires each callee to be annotated with the `Amb` return type. It cannot be used to escape unless the caller is prepared for it to escape. That's a significant limitation (but all we're really saying is that Haskell doesn't support call/cc).
The Haskell version requires each callee to be annotated with the `Amb` return type. It cannot be used to escape unless the caller is prepared for it to escape. That's a significant limitation (but all we're really saying is that Haskell doesn't support call/cc).