[GHC] #14798: Error message suggests applying (non-existant) function to more arguments

[GHC]

#14798: Error message suggests applying (non-existant) function to more arguments
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.5
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Poor/confusing
  Unknown/Multiple                   |  error message
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Applying a constraint that doesn't hold fails, this is expected

 {{{
 $ ~/code/qc-ghc/inplace/bin/ghc-stage2 --interactive -ignore-dot-ghci
 GHCi, version 8.5.20180128: http://www.haskell.org/ghc/  :? for help
 Prelude> :set -XGADTs -XConstraintKinds -XTypeApplications
 Prelude> data Dict c where Dict :: c => Dict c
 Prelude> data A
 Prelude> :t Dict @(Eq A)

 <interactive>:1:1: error:
     No instance for (Eq A) arising from a use of ‘Dict’
 }}}

 but for `(Eq (Int -> Int))` GHC additionally suggests maybe applying a
 function (what function?) to more arguments

 {{{
 Prelude> :t Dict @(Eq (Int -> Int))

 <interactive>:1:1: error:
     No instance for (Eq (Int -> Int)) arising from a use of ‘Dict’
       (maybe you haven't applied a function to enough arguments?)
 Prelude>
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14798>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler