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|
module Util
( accumulate
, intersperse
, joinBy
, nullToMaybe
, firstJust
, splitBy
) where
swap :: (a, b) -> (b, a)
swap (a, b) = (b, a)
-- Accumulate all sub-sequences,
-- For example, accumulate [1,2,3] == [[1], [1, 2], [1, 2, 3]]
accumulate :: [a] -> [[a]]
accumulate [] = []
accumulate (x:xs) = (x:) <$> ([]:accumulate xs)
-- Insert element at every other position of list
intersperse :: a -> [a] -> [a]
intersperse _ [] = []
intersperse _ [x] = [x]
intersperse y (x:xs) = x : y : intersperse y xs
joinBy :: Monoid a => a -> [a] -> a
joinBy delim lst = mconcat $ intersperse delim lst
splitBy' :: Eq a => a -> [a] -> ([a], [a])
splitBy' _ [] = ([], [])
splitBy' delim (x:xs)
| delim == x = (xs, [])
| otherwise = (x:) <$> splitBy' delim xs
splitBy :: Eq a => a -> [a] -> ([a], [a])
splitBy d = swap . splitBy' d
nullToMaybe :: (Eq a, Monoid a) => a -> Maybe a
nullToMaybe m
| m == mempty = Nothing
| otherwise = Just m
firstJust :: a -> [Maybe a] -> a
firstJust x [] = x
firstJust _ (Just x:_) = x
firstJust x (_:xs) = firstJust x xs
|
