blob: fe6730b9322413b783476742673bea090423131f (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
|
-- | A module containing a box datatype representing a compiled item. This
-- item can be of any type, given that a few restrictions hold (e.g. we want
-- a 'Typeable' instance to perform type-safe casts).
--
{-# LANGUAGE ExistentialQuantification #-}
module Hakyll.Core.CompiledItem
( CompiledItem (..)
, compiledItem
, unCompiledItem
) where
import Data.Binary (Binary)
import Data.Typeable (Typeable, cast)
import Data.Maybe (fromMaybe)
import Hakyll.Core.Writable
-- | Box type for a compiled item
--
data CompiledItem = forall a. (Binary a, Typeable a, Writable a)
=> CompiledItem a
instance Writable CompiledItem where
write p (CompiledItem x) = write p x
-- | Box a value into a 'CompiledItem'
--
compiledItem :: (Binary a, Typeable a, Writable a)
=> a
-> CompiledItem
compiledItem = CompiledItem
-- | Unbox a value from a 'CompiledItem'
--
unCompiledItem :: (Binary a, Typeable a, Writable a)
=> CompiledItem
-> a
unCompiledItem (CompiledItem x) = fromMaybe error' $ cast x
where
error' = error "Hakyll.Core.CompiledItem.unCompiledItem: Unsupported type"
|
