Haskell List Appending
Created at 2016-04-23T19:00:21.000Z

Of course, right part of list is not evaluated until left part of list is finished to be shown. (ref)

λ> print $ "123" ++ "456"
"123456"
λ> print $ "123" ++ undefined
"123*** Exception: Prelude.undefined
λ> print $ [1, 2, 3] ++ [4, 5, 6]
[1,2,3,4,5,6]
λ> print $ [1, 2, 3] ++ [undefined, 4, 5, 6]
[1,2,3,*** Exception: Prelude.undefined
λ> print $ [1, 2, 3] ++ undefined
[1,2,3*** Exception: Prelude.undefined