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text/tests/SlowFunctions.hs
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1{-# LANGUAGE BangPatterns #-}
3module SlowFunctions
4 (
5 indices
6 , splitOn
7 ) where
9import qualified Data.Text as T
10import Data.Text.Internal (Text(..))
11import Data.Text.Unsafe (iter_, unsafeHead, unsafeTail)
13indices :: T.Text -- ^ Substring to search for (@needle@)
14 -> T.Text -- ^ Text to search in (@haystack@)
15 -> [Int]
16indices needle@(Text _narr _noff nlen) haystack@(Text harr hoff hlen)
17 | T.null needle = []
18 | otherwise = scan 0
19 where
20 scan i | i >= hlen = []
21 | needle `T.isPrefixOf` t = i : scan (i+nlen)
22 | otherwise = scan (i+d)
23 where t = Text harr (hoff+i) (hlen-i)
24 d = iter_ haystack i
26splitOn :: T.Text -- ^ Text to split on
27 -> T.Text -- ^ Input text
28 -> [T.Text]
29splitOn pat src0
30 | T.null pat = error "splitOn: empty"
31 | l == 1 = T.split (== (unsafeHead pat)) src0
32 | otherwise = go src0
33 where
34 l = T.length pat
35 go src = search 0 src
36 where
37 search !n !s
38 | T.null s = [src] -- not found
39 | pat `T.isPrefixOf` s = T.take n src : go (T.drop l s)
40 | otherwise = search (n+1) (unsafeTail s)