#16314: Improve confusing error message with MINIMAL pragma -------------------------------------+------------------------------------- Reporter: lerkok | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 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 simonpj):
it would be nice to get a warning right where the class is defined, as opposed to where it is instantiated.
I'm not sure that would be a good change. Here's a typical use-case (taken from the user manual) {{{ class Eq a where (==), (/=) :: a -> a -> Bool (==) a b = not (a /= b) (/=) a b = not (a == b) {-# MINIMAL (==) | (/=) #-} }}} Both have default methods, but you must define one or the other, or you get an infinite loop. At an instance we specifically want a warning, even though both have default methods. This was the original motivation for MINIMAL. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16314#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler