Blow your mind
Revision as of 02:23, 1 March 2006 by JohannesAhlmann (talk | contribs)
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Helpful Idioms
-- splitting in twos (alternating)
-- "1234567" -> ("1357", "246")
foldr (\a (x,y) -> (a:y,x)) ("","") "1234567"
-- splitting in N -- 2 -> "1234567" -> ["12", "34", "56", "7"] fst . until (null . snd) (\(a,b) -> let (x,y) = splitAt 2 b in (a++[x],y)) $ ([], [1..7])
-- combinations -- "12" -> "45" -> ["14", "15", "24", "25"] sequence ["12", "45"]
-- factorial -- 6 -> 720 product [1..6] foldl1 (*) [1..6] (!!6) $ unfoldr (\(n,f) -> Just (f, (n+1,f*n))) (1,1)
-- split at whitespace -- "hello world" -> ["hello","world"] words "hello world"
-- interspersing with newlines -- ["hello","world"] -> "hello world" unlines ["hello","world"] intersperse '\n' ["hello","world"]
-- zweierpotenzen iterate (*2) 1 unfoldr (\z -> Just (z,2*z)) 1