#13249: Default signature check can be quite onerous -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #12918 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Well it's true, isn't it? We are simply listing the conditions under which you can use the generic default instance. The more constraints you need, the less generally-applicable it is. In this case you are saying that you can say {{{ instance MonadGet ty where type Remaining ty = blah -- no code for 'remaining' }}} only if: * `ty` is of form `(t n)` * We have `MonadTrans t, MonadGet n, Monad n` * `Remaining (t n)` equals `Remaining n`. Fair enough -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13249#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler