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[FIX] double -> int for hyper data dates info.
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1 {-# LANGUAGE ExistentialQuantification #-}
2
3 -- | Thanks to Gabriel Gonzales and his beautiful folds
4
5 import Data.Monoid
6 import Prelude hiding (head, last, all, any, sum, product, length)
7
8 import qualified Data.Foldable
9
10 data Fold i o = forall m . Monoid m => Fold (i -> m) (m -> o)
11
12 fold :: Fold i o -> [i] -> o
13 fold (Fold tally summarize) is = summarize (reduce (map tally is))
14 where
15 reduce = Data.Foldable.foldl' (<>) mempty
16
17 --
18 head :: Fold a (Maybe a)
19 head = Fold (First . Just) getFirst
20
21 last :: Fold a (Maybe a)
22 last = Fold (Last . Just) getLast
23 --
24 all :: (a -> Bool) -> Fold a Bool
25 all predicate = Fold (All . predicate) getAll
26
27 any :: (a -> Bool) -> Fold a Bool
28 any predicate = Fold (Any . predicate) getAny
29 --
30 sum :: Num n => Fold n n
31 sum = Fold Sum getSum
32
33 product :: Num n => Fold n n
34 product = Fold Product getProduct
35
36 length :: Num n => Fold i n
37 length = Fold (\_ -> Sum 1) getSum
38
39 --
40 {-# LANGUAGE BangPatterns #-}
41
42 data Average a = Average { numerator :: !a, denominator :: !Int }
43
44 instance Num a => Monoid (Average a) where
45 mempty = Average 0 0
46 mappend (Average xL nL) (Average xR nR) = Average (xL + xR) (nL + nR)
47
48 average :: Fractional a => Fold a a
49 average = Fold tally summarize
50 where
51 tally x = Average x 1
52 summarize (Average numerator denominator) =
53 numerator / fromIntegral denominator
54
55
56