Printing patterns in Haskell

Write a function Int -> Char -> Char -> [String] that will create the appropriate pattern.

For example: mapM_ putStrLn (pattern 48 '.' '+')
................................................
.+..+..+..+..+..+..+..+..+..+..+..+..+..+..+..+.
+.++.++.++.++.++.++.++.++.++.++.++.++.++.++.++.+
................................................


This idea is inspired by Writing nested for loops to produce certain output (but more general).

I am pretty satisfied with my code to solve this problem:
pattern :: Int -> Char -> Char -> [String]
pattern len a b = map (take len . cycle) [[a], [a, b, a], [b, a, b], [a]]

main :: IO()
main = mapM_ putStrLn (pattern 48 '.' '+')


Seems fine. However, depending on the context and the rest of the program, you can relax pattern's type:

pattern :: Int -> a -> a -> [[a]]

Also, since every putStrLn is basically hPutStrLn stdout, you could first glue all lines together with unlines and then print them with a single action:

main = putStr (unlines (pattern 48 '.' '+'))

StackExchange Code Review Q#111961, answer score: 5