#8912: Documentation stale: implicit-parameter constraints seem to be allowed in instance declarations now. -------------------------------------+------------------------------------- Reporter: | Owner: andreas.abel | Status: closed Type: bug | Milestone: Priority: normal | Version: 7.6.3 Component: | Keywords: implicit- Documentation | parameter instance-constraints Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: | Blocked By: Documentation bug | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dimitris): But it's a useful feature, although arguably a bit dangerous to use ... For instance I am working with a library that someone else has written that exposes only a type-class based interface, i.e. you provide instances of certain classes. Now these classes provide -- sadly -- only a functional interface, so the only way for me to parameterize my instance implementation is to use a class instance context. But if that context can't itself be an implicit parameter or its instances depend on an implicit parameter then it's pretty impossible to reconfigure my code! So I think there is a pretty compelling case to /omit/ that check and perhaps warn users that this may lead to unpredictable behaviour. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8912#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler