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    Can somebody explain to me why the following works:

    add2 = foldr (\ x xs -> x + 2 : xs) []


    but this does not:

    appendTest = foldr(\ x xs -> x ++ "Test" : xs) []


    I get a type mismatch between [[[Char]]] and [[Char]] when I call

    appendTest ["one", "two"]


    I need to do it this way:


    appendTest = foldr(\ x xs -> (\ x -> x++ "Test") : xs) []


    I am not sure why though, especially since the Int example works. Sure, String is [Char], but I can't see why the first version of appendTest expects a [[[Char]]] instead of a [[Char]].


    Thanks a lot!