[GHC] #10224: Partial type signatures generate typed hole warnings

31 Mar 2015

      #10224: Partial type signatures generate typed hole warnings
-------------------------------------+-------------------------------------
              Reporter:  quchen      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:  7.10.2
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  Incorrect
  Unknown/Multiple                   |  warning at compile-time
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 GHCi generates typed hole warnings in type signatures even when
 PartialTypeSignatures is enabled:

 {{{
...
:set -XPartialTypeSignatures
...
:t (==) :: Char -> _
 <interactive>:1:17: Warning:
     Found hole ‘_’ with type: Char -> Bool
     In an expression type signature: Char -> _
     In the expression: (==) :: Char -> _
 (==) :: Char -> _ :: Char -> Char -> Bool
...
:set -XNoPartialTypeSignatures
...
:t (==) :: Char -> _
 <interactive>:1:17:
     Found hole ‘_’ with type: Char -> Bool
     To use the inferred type, enable PartialTypeSignatures
     In an expression type signature: Char -> _
     In the expression: (==) :: Char -> _
 }}}
Similarly, GHC 7.10.1, when given the following source,

 {{{
 {-# LANGUAGE PartialTypeSignatures #-}

 f = (==) :: Char -> _

 main = return ()
 }}}

 mentions that it "found a hole".

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10224
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler