#14363: :type hangs on coerce -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: | -------------------------------------+------------------------------------- Description changed by Iceland_jack: Old description:
This works
{{{ ghci -ignore-dot-ghci GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Prelude> import Data.Coerce Prelude Data.Coerce> :t [fmap, coerce]
<interactive>:1:8: error: • Occurs check: cannot construct the infinite type: b ~ f b arising from a use of ‘coerce’ • In the expression: coerce In the expression: [fmap, coerce]
}}}
But doing it with `contra`
{{{ Prelude Data.Coerce> contra = undefined :: Functor f => (b -> a) -> (f a -> f b) }}}
it hangs
{{{ Prelude Data.Coerce> :t [coerce, contra] ^CInterrupted. Prelude Data.Coerce> :t [contra, coerce] ^CInterrupted. }}}
New description: This works {{{ $ ghci -ignore-dot-ghci GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Prelude> import Data.Coerce Prelude Data.Coerce> :t [fmap, coerce] <interactive>:1:8: error: • Occurs check: cannot construct the infinite type: b ~ f b arising from a use of ‘coerce’ • In the expression: coerce In the expression: [fmap, coerce] }}} But doing it with `contra` {{{ Prelude Data.Coerce> contra = undefined :: Functor f => (b -> a) -> (f a -> f b) }}} it hangs {{{ Prelude Data.Coerce> :t [coerce, contra] ^CInterrupted. Prelude Data.Coerce> :t [contra, coerce] ^CInterrupted. }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14363#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler