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