10 ways to map a list in haskell

Since haskell is a list-based language, there are many ways to work with lists. This article details some of the most interesting ways to multiply each number in a list by 5.

1. The Imperative way

main:: IO()
main = do
  mutable <- M.replicate 256 1
  forM_ ([1..256] z->
    modify mutable (x->x*5) z
   )

2. The boring way

multiplyList :: [Int] -> [Int]
multiplyList xs = map (\x->x*5) xs

3. currying

multiplyList :: [Int] -> [Int]
multiplyList = map (*5) 

4. monad

multiplyList :: [Int] -> [Int]
multiplyList xs =  xs >>= (\x -> [x*5])

5. short functor

m=(<$>)(*5)

6. List comprehension

multiplyList :: [Int] -> [Int]
multiplyList xs = [x*5 | x <- xs]

7. Do notation

multiplyList :: [Int] -> [Int]
multiplyList xs = do
    x <- xs
    return $ x*5

8. Functor

multiplyList :: [Int] -> [Int]
multiplyList xs = fmap (\x -> x*5) xs

9. Applicative

multiplyList :: [Int] -> [Int]
multiplyList xs =  pure (\x->x*5) <*> xs

10. Recursion

multiplyList :: [Int] -> [Int]
multiplyList [] = []
multiplyList (x:xs) = (x*5) : multiplyList xs