mirror of
https://code.naskya.net/repos/ndqEd
synced 2025-01-11 03:36:47 +09:00
32 lines
977 B
Haskell
32 lines
977 B
Haskell
{- This file is part of Vervis.
|
|
-
|
|
- Written in 2016 by fr33domlover <fr33domlover@riseup.net>.
|
|
-
|
|
- ♡ Copying is an act of love. Please copy, reuse and share.
|
|
-
|
|
- The author(s) have dedicated all copyright and related and neighboring
|
|
- rights to this software to the public domain worldwide. This software is
|
|
- distributed without any warranty.
|
|
-
|
|
- You should have received a copy of the CC0 Public Domain Dedication along
|
|
- with this software. If not, see
|
|
- <http://creativecommons.org/publicdomain/zero/1.0/>.
|
|
-}
|
|
|
|
module Data.HashMap.Lazy.Local
|
|
( flip
|
|
)
|
|
where
|
|
|
|
import Prelude hiding (flip)
|
|
|
|
import Data.Hashable (Hashable)
|
|
|
|
import qualified Data.HashMap.Lazy as M
|
|
|
|
-- | Build a 'M.HashMap' which maps each value in the original HashMap to the
|
|
-- keys under which it appears there.
|
|
flip :: (Eq b, Hashable b) => M.HashMap a b -> M.HashMap b [a]
|
|
flip = M.foldrWithKey collect M.empty
|
|
where
|
|
collect k v = M.insertWith (\ _new old -> k : old) v [k]
|