[ANNOUNCE] GHC 8.6.1-alpha2 available

[Andrés Sicard-Ramírez]

On 15 July 2018 at 20:07, Ben Gamari <ben at well-typed.com> wrote:
>
> The GHC development team is pleased to announce the second alpha release
> leading up to GHC 8.6.1.

The following MVE uses the gitrev library (
http://hackage.haskell.org/package/gitrev ):

$ cat Test.hs

{-# LANGUAGE TemplateHaskell #-}

module Main where

import Development.GitRev

commitInfo :: Maybe String
commitInfo = case $(gitHash) of
  "UNKNOWN" -> Nothing
  hash      -> Just hash

main :: IO ()
main = print commitInfo


The MVE compiles *without* warnings with different versions of GHC
(e.g. 8.4.3) but with GHC 8.6.1-alpha2 I get the following warning:

$ ghc Test.hs

Test.hs:10:3: warning: [-Woverlapping-patterns]
    Pattern match is redundant
    In a case alternative: hash -> ...
   |
10 |   hash      -> Just hash
   |   ^^^^^^^^^^^^^^^^^^^^^^
Linking Test ...

Is it a bug or is it the expected behaviour?


Best,


-- 
Andrés