[Haskell-beginners] Stymied by mutable arrays in the ST monad

[Matthew Moppett]

I've been trying to use mutable arrays in the ST monad, and wrote out a
little proof of concept function:

idST :: [Int] -> [Int]
idST xs = runST $ do
    array <- newListArray (1, (length xs)) xs
    return (getElems array)

-- where idSt should be equivalent to id.

And I get the error message:

Couldn't match type `[Int]' with `Int'
    In the return type of a call of `getElems'
    In the first argument of `return', namely `(getElems array)'
    In a stmt of a 'do' block: return (getElems array)

Obviously I'm making a very simple mistake here, but I can't seem to spot
it. Can anyone offer some advice?
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