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by mpartel
3596 days ago
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Structs implementing interfaces can be viewed as subtyping, but they don't have to be. An alternative is to take a typeclass-like view. Basically, a function "(A, A) -> A where A implements I" could be implemented as "(pointer to vtable of interface I, voidptr, voidptr) -> voidptr". Not having "implementation inheritance" between structs helps a lot, though I'm not sure if Go's anonymous fields might pose a problem. |
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Type classes alone don't give you anything like Go's interfaces.
Type classes plus existentials give you something kinda like Go's interfaces, but requires explicit casts (in the form of unwrapping the contents of an existential constructor and putting them into another existential constructor).
Type classes plus rank-N types can express Go's interfaces, but at that point Haskell already has subtyping, induced by subclasses. (Or else how do you think “a Lens is a Traversal” is possible?)