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

On Jun 5, 2017, at 10:48 PM, Anthony Clayden 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. Richard