I know the type signature of (++), I'm just not seeing `n` as a list, I suppose. I'm reading it as being the Int that is passed to splitAt, though perhaps my thought process is just wonky. On Jun 26, 2011, at 6:41 PM, Mike Meyer wrote:

On Sun, 26 Jun 2011 18:14:44 -0400 Jack Henahan wrote:

...

I have this code snippet:

import Data.List

aaa x (y:ys) = case splitAt x (y:ys) of (n, x:xs) -> x:n ++ xs (n, xs) -> n ++ xs

I understand what it's meant to do (that is, split a list at index `x` and make a new list with that element at the head, or just return the list when given a singleton), but my brain is failing me when trying to read the notation `n ++ xs`.

Is there some obvious explanation that I'm just forgetting?

Yes. But more importantly, you're forgetting that you can ask the REPL:

Prelude> :t (++) (++) :: [a] -> [a] -> [a]

So it takes two lists and produces a new one. Trying it:

Prelude> [1, 2, 3] ++ [4, 5, 6] [1,2,3,4,5,6]

So ++ concatenates it's operands.

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