#13401: GHCi gives conflicting information about visible type application -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.1 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: -------------------------------------+------------------------------------- From the docs for `-XVisibleTypeApplication`:
When printing types with `-fprint-explicit-foralls` (page 72) enabled, type variables not available for visible type application are printed in braces. Thus, if you write `myLength = length` without a type signature, `myLength`‘s inferred type will be `forall {f} {a}. Foldable f => f a -> Int`.
{{{
:set -XScopedTypeVariables :set -XTypeApplications :set -fprint-explicit-foralls let foo :: forall a. a; foo = undefined (LINE 1) :t foo foo :: forall {a}. a (LINE 2)
:t (foo @Bool) (foo @Bool) :: Bool (LINE 3) }}}
Type application with `foo` (LINE 1) should be possible, but GHCi claims it is not (LINE 2), then allows it anyway (LINE 3). This looks like a bug with `fprint-explicit-foralls` in detecting which variables are available for type application. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13401 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler