I&#39;ve been trying to use mutable arrays in the ST monad, and wrote out a little proof of concept function:<div><br></div><div><div>idST :: [Int] -&gt; [Int]</div><div>idST xs = runST $ do</div><div>    array &lt;- newListArray (1, (length xs)) xs</div>
<div>    return (getElems array)</div></div><div><br></div><div>-- where idSt should be equivalent to id.</div><div><br></div><div>And I get the error message: </div><div><br></div><div><div>Couldn&#39;t match type `[Int]&#39; with `Int&#39;</div>
<div>    In the return type of a call of `getElems&#39;</div><div>    In the first argument of `return&#39;, namely `(getElems array)&#39;</div><div>    In a stmt of a &#39;do&#39; block: return (getElems array)</div></div>
<div><br></div><div>Obviously I&#39;m making a very simple mistake here, but I can&#39;t seem to spot it. Can anyone offer some advice?</div>