I'd imagine it isn't, at least depending on how you define API compatibility, and whether you're only looking at the API interfaces. Imagine two versions of a library that implement the function "add".
Version 1:
add Int -> Int -> Int
add x y = x + y
Version 2:
add Int -> Int -> Int
add x y = x * y
Both versions expose the same API interface, but the functions that conform to that interface are semantically different. A stronger type system could probably differentiate between the two functions, but I doubt you could generally compute whether both functions implement the same behavior.
Perhaps with some sort of functional extensionality you'd be able to compute compatibility perfectly, but I can't imagine that ever being feasible in practice.
That being said, what Elm does offer is still a huge improvement over humans trying to guess whether they made any breaking changes :)
Perhaps with some sort of functional extensionality you'd be able to compute compatibility perfectly, but I can't imagine that ever being feasible in practice.
That being said, what Elm does offer is still a huge improvement over humans trying to guess whether they made any breaking changes :)