src/Hakyll/Core/Writable/WritableTuple.hs · hakyll

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1-- | This module exposes a writable type 'WritableTuple' which is a simple

2-- newtype wrapper around a tuple.

3--

4-- The idea is that, given a tuple @(a, b)@, @a@ is the value you actually want

5-- to save to the disk, and @b@ is some additional info that you /don't/ want to

6-- save, but that you need later, for example in a 'require' clause.

7--

8{-# LANGUAGE GeneralizedNewtypeDeriving, DeriveDataTypeable #-}

9module Hakyll.Core.Writable.WritableTuple

10 ( WritableTuple (..)

11 , writableTupleFst

12 , writableTupleSnd

13 , writableTupleCompiler

14 ) where

16import Control.Arrow (arr)

18import Data.Typeable (Typeable)

19import Data.Binary (Binary)

21import Hakyll.Core.Writable

22import Hakyll.Core.Compiler

24newtype WritableTuple a b = WritableTuple {unWritableTuple :: (a, b)}

25 deriving (Show, Eq, Ord, Binary, Typeable)

27instance Writable a => Writable (WritableTuple a b) where

28 write dst (WritableTuple (x, _)) = write dst x

30writableTupleFst :: WritableTuple a b -> a

31writableTupleFst = fst . unWritableTuple

33writableTupleSnd :: WritableTuple a b -> b

34writableTupleSnd = snd . unWritableTuple

36writableTupleCompiler :: Compiler (a, b) (WritableTuple a b)

37writableTupleCompiler = arr WritableTuple