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Lists

module Main where

Lists are arbitrary length sequences of elements of the same type. The operator (:) prepends an element to a list. The operator (++) concatenates two lists. The operator (!!) selects an element of a list, counting from zero. length returns the length of a list.

(:) ∷ a → [a] → [a]
(++) ∷ [a] → [a] → [a]
(!!) ∷ [a] → Int → a
length ∷ [a] → Int

ends ∷ [a] → [a]
ends x = [ x !! 0, x !! (length x - 1) ]

y ∷ [Int]
y = 1 : [2,3] ++ [4,5]

main ∷ IO ()
main = mapM_ print [y, ends y]

[1,2,3,4,5]
[1,5]

Main.hs