[Haskell-cafe] [ghc-proposals/cafe] Partially applied type families

Richard Eisenberg rae at cs.brynmawr.edu
Tue Jun 6 19:22:45 UTC 2017

> On Jun 5, 2017, at 10:48 PM, Anthony Clayden <anthony_clayden at clear.net.nz> wrote:
> It was trying to show:
> with CTFs (and presumably closed classes)
> there's an explicit or implicit TypeError catch-all instance
> at the end of the chain of `else`s.
> (It seems InstanceChain `fails` doesn't suffer this.)

As I understand it: You've said that TypeError doesn't work for you. I asked why, looking for a concrete example of how things go wrong. I do see your example of why instance guards can help (already convinced there)... but I still don't see why TypeError is problematic once we have instance guards.


More information about the Haskell-Cafe mailing list