Partial Isomorphism - Hacker Log

Welcome to the Functional Programming Zulip Chat Archive. You can join the chat here.

Sridhar Ratnakumar

Really curious about the best way to do isomorphism check, but with allowance for Maybe:

encodeRoute :: r -> FilePath
decodeRoute :: FilePath -> Maybe r

decodeRoute . encodeRoute = id in principle, but that Maybe is preventing us from treating this as isomorphism. What can be done here?

Sridhar Ratnakumar


-- | An Iso that is not necessarily surjective; as well as takes an (unchanging)
-- context value.
type PartialIso ctx s a = (ctx -> a -> s, ctx -> s -> Maybe a)

partialIsoIsLawful :: PartialIso ctx s a -> ctx -> [a] -> Bool
partialIsoIsLawful (to, from) ctx =
  all $ \a -> let s = to ctx a in Just a == from ctx s
Sridhar Ratnakumar

I think that paper will obviate needing a partialIsoIsLawful.

If I treat decoding routes as parsing, and encoding route as pretty-printing - that paper is super relevant to this problem.

Sridhar Ratnakumar
isJust :: Maybe () <-> Bool
isJust = [biCase|
    Just () <-> True
    Nothing <-> False

whoa - this could be used defined bijecetive route encoders?