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|
module Common
( toLower
, trim
, trimWith
, splitOn
, split2
, replace
, (!!?)
, findVal
, maybeAt
, startsWith
, delete
)
where
import Data.Char (isSpace)
import qualified Data.Char as C
import Data.List (find, stripPrefix)
import Intro
trim :: String -> String
trim = f . f
where
f = reverse . dropWhile isSpace
trimWith :: (Char -> Bool) -> String -> String
trimWith p = f . f
where
f = reverse . dropWhile p
splitOn :: (a -> Bool) -> [a] -> [[a]]
splitOn p s = case dropWhile p s of
[] -> []
s' -> w : splitOn p s''
where
(w, s'') = break p s'
split2 :: (a -> Bool) -> [a] -> ([a], [a])
split2 p s =
case break p s of
(x, _ : y) -> (x, y)
(x, []) -> (x, [])
infix 9 !!?
(!!?) :: [a] -> Int -> Maybe a
(!!?) xs i
| i < 0 = Nothing
| otherwise = go i xs
where
go :: Int -> [a] -> Maybe a
go 0 (x : _) = Just x
go j (_ : ys) = go (j - 1) ys
go _ [] = Nothing
maybeAt :: Int -> [a] -> Maybe a
maybeAt = flip (!!?)
toLower :: String -> String
toLower = fmap C.toLower
startsWith :: (a -> Bool) -> [a] -> Bool
startsWith _ [] = False
startsWith p (x : _) = p x
findVal :: (a -> Bool) -> [(a, b)] -> Maybe b
findVal p xs = snd <$> find (p . fst) xs
replace :: (Eq a) => [a] -> [a] -> [a] -> [a]
replace [] to xs = go xs
where
go [] = to
go (x : xs') = to ++ x : go xs'
replace from to xs | Just xs' <- stripPrefix from xs = to ++ replace from to xs'
replace from to (x : xs) = x : replace from to xs
replace _ _ [] = []
delete :: (a -> Bool) -> [a] -> (Maybe a, [a])
delete p = foldr f (Nothing, [])
where
f x (Nothing, xs) | p x = (Just x, xs)
f x (m, xs) = (m, x : xs)
|
