Initial commit

1 files changed, 82 insertions, 0 deletions

diff --git a/src/Common.hs b/src/Common.hs
new file mode 100644
index 0000000..91bf708
--- /dev/null
+++ b/src/Common.hs
@@ -0,0 +1,82 @@
+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)