#10939: Odditites regarding Any and typeclasses. -------------------------------------+------------------------------------- Reporter: mniip | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | -------------------------------------+------------------------------------- The typechecker seems to be unable to operate on contexts containing "naked" `Any`, for example: {{{#!hs x :: State [Any] () x = put [] }}} {{{ No instance for (MonadState [Any] (StateT [Any] Identity)) arising from a use of ‘put’ }}} A more minimal self-contained example would be: {{{#!hs {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-} import GHC.Prim (Any) class Class a b where method :: a -> b instance Class a a where method = id x :: Any -> Any x = method }}} {{{ No instance for (Class Any Any) arising from a use of ‘method’ }}} It's quite obvious why this error happens (`Any` is not a datatype), however it also feels like it shouldn't happen. All of the above code seems to work in 7.8, which is back when `Any` was a datatype. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10939 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler