praxis

Various programming exercises.
git clone git://git.jtobin.io/praxis.git
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Matches.hs (301B)

      1 
      2 module Matches where
      3 
      4 import Control.Monad
      5 
      6 appears :: Eq a => [a] -> [a] -> Int
      7 appears = go where
      8   go [] _ = 1
      9   go _ [] = 0
     10   go ab@(b:bs) (c:cs)
     11     | b == c    = appears bs cs + appears ab cs
     12     | otherwise = appears ab cs
     13 
     14 appears' n = length . filter (== n) . filterM (const [True, False])
     15