#9674: Foldable doesn't have any laws -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: task | Status: new Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.8.3 Libraries | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: Documentation bug | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by ekmett): `foldMap f = fold . fmap f` assumes you have a `Functor` instance as well, so any such law would need that caveat. `fold = foldMap id` holds universally. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9674#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler