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module Main where

There are various ways that we can combine and output several strings.

first, second, third ∷ String

first = "hello"
second = "there"
third = "world"

We can use map to apply endline to each element of a list. map has the type

map ∷ (a → b) → [a] → [b]

where a and b are type variables. hello is now a list of strings.

endline ∷ String → String
endline = (++ "\n")

hello ∷ [String]
hello = map endline [first, second, third]

concat concatenates our lists into a single string.

concat ∷ [[a]] → [a]

main ∷ IO ()
main = putStr $ concat hello

hello
there
world

Main.hs