strange behaviors when case splitting on `List` and local items

[raptazure]

• Case splitting on _ with type List a gives List _ instead of Nil and x : xs.
• Case splitting on local items doesn't work at first. It seems that treating typed holes as errors can prevent case splitting.

Like this video shows:

2021-02-16.18.19.46.mp4

It would be great for type-driven development if case splitting works better. Thanks!

[nwolverson]

As far as I can see this is just down to the way case splitting works in purs ide - and should be raised as an issue in the compiler repo. Holes as errors - yeah if you've not managed to build the file before, there won't be any type info for ColorTy, not sure if that's what you're seeing there.

@kritzcreek can you shed any light on what's happening with that List case split - looks to me like Maybe a case splits fine, but List a gives (List _) even though List is not a type constructor - some issue with recursive datatypes?

[kritzcreek]

Yeah that looks like purescript/purescript#3053. It's finding Lazy.List which just a newtype and it case splits on that. Case-splitting could probably use a proper re-write but I don't have time for it anytime soon.

[raptazure]

Ah, thanks! :)

[nwolverson]

Ah @kritzcreek yes that looks to be it, worth noting you don't even need anything of Data.List imported for that to happen - it occurs even with a local List declaration - but changing to MyList works fine