Unused type variables with non-linear patterns
Jan Stolarek
jan.stolarek at p.lodz.pl
Thu Dec 10 14:48:59 UTC 2015
An intersting thing came up when implementing warnings for unused type variables in type family
patterns (#10982 / D1576):
type family X a b where
X a a = Int
Should we emit a warning that `a` is unused? It does not appear in the RHS but it is actually used
because of non-linear pattern. We can fix this by prefixing both appearances of `a` with an
underscore - this silences the warning and maintains semantics. Nevertheless, if a variable is
unused it should be perfectly valid to replace it with an underscore - that is not the case in
this example. Thoughts?
Janek
---
Politechnika Łódzka
Lodz University of Technology
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