blob: 762d8fb872e870cc7f78f70e85f55056b909e873 (
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
41
|
{-# LANGUAGE GeneralizedNewtypeDeriving, FlexibleInstances #-}
module Sized where
import Data.Monoid
newtype Size = Size Int
deriving (Eq, Ord, Show, Num)
getSize :: Size -> Int
getSize (Size i) = i
class Sized a where
size :: a -> Size
instance Sized Size where
size = id
-- This instance means that things like
-- (Foo, Size)
-- (Foo, (Bar, Size))
-- ...
-- are all instances of Sized.
instance Sized b => Sized (a,b) where
size = size . snd
-- Since (<>) has been moved from Monoid to Semigroup, this little change is required
-- Old version
{-
instance Monoid Size where
mempty = Size 0
mappend = (+)
-}
-- New version
instance Monoid Size where
mempty = Size 0
instance Semigroup Size where
(<>) = (+)
|