
30 Sep
2015
30 Sep
'15
6:26 p.m.
On 09/30/2015 08:10 PM, David Feuer wrote:
The Eq constraint is needed to support pattern matching, the raison d’être of pattern synonyms. I'm pretty sure the reason you need ScopedTypeVariables for your second example is that GHC only allows pattern signatures with that extension enabled. Once upon a time there was a separate PatternSignatures extension, I believe, but not any more.
Perhaps ScopedTypeVariables by default (or only?) would be relevant for the revamped[1] Haskell' committee? Would there be any actual downsides? It's always seemed to me that ScopedTypeVariables was the way it should have been from the start (given perfect foresight). Regards, [1] http://permalink.gmane.org/gmane.comp.lang.haskell.prime/3965