#15459: Wredundant-constraints does not work when constraint synonym is used -------------------------------------+------------------------------------- Reporter: flip101 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: 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 flip101): Simon, i don't know about type families. I tried reading about them at https://wiki.haskell.org/GHC/Type_families but even so i don't feel i have enough experience with them to give a useful response to your question. It's also more confusing for me because in your example foo doesn't have an implementation. With `withoutWarning = sort` it was clear to me that sort requires Ord but not Show. I will make a guess here and say "yes i expect a warning for that". When the instance `F [a]` is used in used in the function `foo` it can be deduced that this is the is the active instance which is used in the function foo. If foo is implemented as `foo = sort` then (`Show a`) is also redundant in the instance of the .. constraint type family ? My guess can be non-sense .. please refer to the first paragraph :P -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15459#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler