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|
{- Some stuff from Prelude should not be used, as it tends to be a source
- of bugs.
-
- This exports functions that conflict with the prelude, which avoids
- them being accidentially used.
-}
module Utility.BadPrelude where
{- read should be avoided, as it throws an error -}
read :: Read a => String -> a
read = Prelude.read
{- head is a partial function; head [] is an error
- Instead, use: take 1 or headMaybe -}
head :: [a] -> a
head = Prelude.head
{- tail is also partial
- Instead, use: drop 1 -}
tail :: [a] -> [a]
tail = Prelude.tail
{- init too
- Instead, use: beginning -}
init :: [a] -> [a]
init = Prelude.init
{- last too
- Instead, use: end or lastMaybe -}
last :: [a] -> a
last = Prelude.last
{- Like head but Nothing on empty list. -}
headMaybe :: [a] -> Maybe a
headMaybe [] = Nothing
headMaybe v = Just $ Prelude.head v
{- Like last but Nothing on empty list. -}
lastMaybe :: [a] -> Maybe a
lastMaybe [] = Nothing
lastMaybe v = Just $ Prelude.last v
{- All but the last element of a list.
- (Like init, but no error on an empty list.) -}
beginning :: [a] -> [a]
beginning [] = []
beginning (x:xs) = beginning' x xs
where
beginning' _ [] = []
beginning' y (z:zs) = y : beginning' z zs
{- Like last, but no error on an empty list. -}
end :: [a] -> [a]
end [] = []
end (x:xs) = end' x xs
where
end' y [] = [y]
end' _ (y:ys) = end' y ys
|
