> On at Apr 29 05:55:14 UTC 2017, Anthony Clayden wrote: > ... > So should I reasonably have known that > a superclass constraint > with FunDeps on the superclass > induces FunDeps on the sub-class > without explicitly needing to declare so? > > (I'm not complaining, more surprised/impressed.) >
From experimenting, FunDeps seem to come through from a superclass of a superclass of a superclass of the class. This from David Feuer says http://stackoverflow.com/questions/35252562/find-an-element-in-an-hlist/35260970#35260970 "superclass context is critical .... GHC always commits to an instance before checking the instance constraints, but it doesn't even try to find an instance until after solving the superclass constraints. So we need to use the superclass constraint to fix ..." Presumably that's the mechanism that induces FunDeps from supeclass constraints. Is that behaviour officially documented somewhere? (I remember when Type Families and (~) Constraints were first released, they weren't available superclass. Then there were a couple of releases you could put superclass constraints, but they weren't effective.) AntC _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
