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| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2016-11-06 09:09:36 -0500 |
|---|---|---|
| committer | Ryan Scott <ryan.gl.scott@gmail.com> | 2016-11-06 09:09:36 -0500 |
| commit | 630d88176e8dd3ccc269451bca8f55398ef5265c (patch) | |
| tree | 71660e73c5e770ee83a1bbad4452a0d23e20f42a /compiler/utils/Util.hs | |
| parent | 25c8e80eccc512d05c0ca8df401271db65b5987b (diff) | |
| download | haskell-630d88176e8dd3ccc269451bca8f55398ef5265c.tar.gz | |
Allow GeneralizedNewtypeDeriving for classes with associated type families
Summary:
This implements the ability to derive associated type family instances
for newtypes automatically using `GeneralizedNewtypeDeriving`. Refer to the
users' guide additions for how this works; I essentially follow the pattern
laid out in https://ghc.haskell.org/trac/ghc/ticket/8165#comment:18.
Fixes #2721 and #8165.
Test Plan: ./validate
Reviewers: simonpj, goldfire, austin, bgamari
Reviewed By: simonpj
Subscribers: mpickering, thomie
Differential Revision: https://phabricator.haskell.org/D2636
GHC Trac Issues: #2721, #8165
Diffstat (limited to 'compiler/utils/Util.hs')
| -rw-r--r-- | compiler/utils/Util.hs | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/compiler/utils/Util.hs b/compiler/utils/Util.hs index 5f66b53171..3104c747a1 100644 --- a/compiler/utils/Util.hs +++ b/compiler/utils/Util.hs @@ -47,6 +47,8 @@ module Util ( chunkList, + changeLast, + -- * Tuples fstOf3, sndOf3, thdOf3, firstM, first3M, @@ -571,6 +573,12 @@ chunkList :: Int -> [a] -> [[a]] chunkList _ [] = [] chunkList n xs = as : chunkList n bs where (as,bs) = splitAt n xs +-- | Replace the last element of a list with another element. +changeLast :: [a] -> a -> [a] +changeLast [] _ = panic "changeLast" +changeLast [_] x = [x] +changeLast (x:xs) x' = x : changeLast xs x' + {- ************************************************************************ * * |