-- | General shorthands and other small operations. Part of the "Useful" module. module Useful.General where import Data.List -- | Alias of as /= (not equal to) (!=) :: Eq a => a -> a -> Bool (!=) = (/=) -- | Alias of mod (%) = mod -- | Works like python's \"in\" function. (Alias of elem). Simply checks if an item is in a list. -- -- > $ "Hello" ? ["Hello","there","people"] -- > True -- > $ "Bonjour" ? ["Hello","there","people"] -- > False (?) :: Eq a => a -> [a] -> Bool (?) = elem -- | Alias of as isInFixOf. Checks if list is a sublist of another list -- -- > $ "hello" ?? "Why hello there people" -- > True -- > $ [2,3] ?? [1,2,3,4] -- > True -- > $ "bonjour" ?? "why hello there people" -- > False (??) :: Eq a => [a] -> [a] -> Bool (??) = isInfixOf -- | Returns the index of the first occurance of an item if it is in a list. Otherwise gives an error. Also remember, starts counting from 0! -- -- NOTE: This is not like elemIndex! It does not return a Maybe Int it returns an error if the item is not in a list. Either use elemIndex or test using ? first. THIS FUNCTION IS NOT COMPLETE. -- -- > $ 'n' ?! "banana" -- > 2 -- > $ 'v' ?! "banana" -- > *** Exception: Item not in list (?!) :: Eq a => a -> [a] -> Int (?!) x y = f x y 0 where f :: Eq a => a -> [a] -> Int -> Int f x [] _ = error "Item not in list" f x (y:ys) c |x == y = c |otherwise = f x ys (c+1) -- | Takes a list and a pair (x,y) and inserts the item y into the list at position x -- -- > $ ["hello","there","people"] !/ (0,"bonjour") -- > ["bonjour","there","people"] (!/) :: [a] -> (Int,a) -> [a] (!/) xs (i,y) |i >= len xs = error "index too large" |otherwise = [if n == i then y else x | (x,n) <- zip xs [0..] ] -- | Like !! but returns Maybe a -- -- > $ [1,2,3,4] ! 5 -- > Nothing -- > $ [1,2,3,4] ! 1 -- > Just 2 (!) :: [a] -> Int -> Maybe a (!) xs i = plingHelper xs i 0 plingHelper [] _ _ = Nothing plingHelper (x:xs) i n |i == n = Just x |otherwise = plingHelper xs i (n+1) -- | alias of length len :: [a] -> Int len = length -- | alias of length count :: [a] -> Int count = length -- | Simple function that takes the unit list and returns the unit -- -- NOTE: Will return an error if not supplied with the unit list -- -- > $ the ["hello"] -- > "hello" -- > $ the ["hello","there"] -- > "*** Exception: function 'the' called with a list other than the unit list. the :: [a] -> a the [x] = x the _ = error "function 'the' called with a list other than the unit list."