module General.Util where
import General.Base
-- | Only append strings if neither one is empty
(++?) :: String -> String -> String
a ++? b = if null a || null b then [] else a ++ b
sortOn f = sortBy (comparing f)
groupOn f = groupBy ((==) `on` f)
nubOn f = nubBy ((==) `on` f)
sortFst mr = sortOn fst mr
groupFst mr = groupOn fst mr
groupFsts :: Eq k => [(k,v)] -> [(k,[v])]
groupFsts = map (fst . head &&& map snd) . groupFst
sortGroupFsts mr = groupFsts . sortFst $ mr
sortGroupFst mr = groupFst . sortFst $ mr
fold :: a -> (a -> a -> a) -> [a] -> a
fold x f [] = x
fold x f xs = fold1 f xs
fold1 :: (a -> a -> a) -> [a] -> a
fold1 f [x] = x
fold1 f xs = f (fold1 f a) (fold1 f b)
where (a,b) = halves xs
halves :: [a] -> ([a],[a])
halves [] = ([], [])
halves (x:xs) = (x:b,a)
where (a,b) = halves xs
merge :: Ord a => [a] -> [a] -> [a]
merge xs [] = xs
merge [] ys = ys
merge (x:xs) (y:ys)
| x <= y = x : merge xs (y:ys)
| otherwise = y : merge (x:xs) ys
mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
mergeBy f xs [] = xs
mergeBy f [] ys = ys
mergeBy f (x:xs) (y:ys)
| f x y /= GT = x : mergeBy f xs (y:ys)
| otherwise = y : mergeBy f (x:xs) ys
merges :: Ord a => [[a]] -> [a]
merges = fold [] merge
mergesBy :: (a -> a -> Ordering) -> [[a]] -> [a]
mergesBy f = fold [] (mergeBy f)
split :: Eq a => a -> [a] -> [[a]]
split x [] = []
split x xs = if null b then [a] else a : split x (tail b)
where (a,b) = break (== x) xs
rep from to x = if x == from then to else x
reps from to = map (rep from to)
-- | Like splitAt, but also return the number of items that were split.
-- For performance.
splitAtLength :: Int -> [a] -> (Int,[a],[a])
splitAtLength n xs = f n xs
where
f i xs | i == 0 = (n,[],xs)
f i [] = (n-i,[],[])
f i (x:xs) = (a,x:b,c)
where (a,b,c) = f (i-1) xs
rbreak f xs = case break f $ reverse xs of
(_, []) -> (xs, [])
(as, b:bs) -> (reverse bs, b:reverse as)
compareCaseless :: String -> String -> Ordering
compareCaseless x = compare (map toLower x) . map toLower
-- compare strings, but with an ordering that puts 'a' < 'A' < 'b' < 'B'
compareString :: String -> String -> Ordering
compareString (x:xs) (y:ys) = case compareChar x y of
EQ -> compareString xs ys
x -> x
compareString [] [] = EQ
compareString xs ys = if null xs then LT else GT
compareChar :: Char -> Char -> Ordering
compareChar x y = case (compare x y, compare (toLower x) (toLower y)) of
(EQ, _) -> EQ
(x, EQ) -> if x == GT then LT else GT
(_, x ) -> x
findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a)
findM p [] = return Nothing
findM p (x:xs) = do
v <- p x
if v then return $ Just x else findM p xs