#14694: Can't coerce given assumptions -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ $ ghci -ignore-dot-ghci GHCi, version 8.5.20180105: http://www.haskell.org/ghc/ :? for help Prelude> newtype WF f a = WF (f a) Prelude> import Data.Coerce Prelude Data.Coerce> :set -XFlexibleContexts Prelude Data.Coerce> :t coerce :: Coercible (cat a b) (a -> f b) => cat a b -> (a -> WF f b) <interactive>:1:1: error: • Couldn't match representation of type ‘cat1 a1 b1’ with that of ‘a1 -> WF f1 b1’ arising from a use of ‘coerce’ • In the expression: coerce :: Coercible (cat a b) (a -> f b) => cat a b -> (a -> WF f b) }}} I'm not sure if I've filed this before or if it's even a bug. But we know that `Coercible (a -> f b) (a -> WF f b)` so why doesn't this work? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14694 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler