The code below is accepted when the extension is disabled, because the identifiers starting with _ are parsed as ordinary type variables. From what I read on the ghc mailing list, the type families should also be accepted with the NamedWildCards on. If so, shouldn't the wildcards be
I also wonder if the warnings in type families should be enabled with
#10982: Warn about unused pattern variables in type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: msosn Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by jstolarek): Replying to [comment:2 msosn]: treated as type variables in the other cases as well? I think you're right. I mean if this code is valid when `NamedWildCards` are turned off, then it certainly should be valid when we enable `NamedWildCards`. After all named wild cards can't possibly appear in any of these declarations, so whenever a name that looks like a wildcard appears we can safely assume that it must be a type variable. Note however, that we only want to generate warnings for unused pattern variables in type families. the -fwarn-unused-matches option or should I make a new flag? I say we use the existing flag. If anyone complains that they want a separate flag for unused type-level patterns then we can add it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10982#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler