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    <p>It appears you have two issues with your <code>insert</code> function.</p> <p>First, your two definitions of the <code>insert</code> function return different things.</p> <pre><code>Set [list] -- Return type here is Collection </code></pre> <p>and</p> <pre><code>[list] ++ numberToInsert -- Return type here is some sort of list, or [a0] </code></pre> <p>So first, you'll need to Make the second version return a <code>Collection</code>:</p> <pre><code>Set ([list] ++ numberToInsert) </code></pre> <p>But this is still wrong, because <code>numberToInsert</code> is not a list, and <code>++</code> concatenates two lists together, so I think you're really wanting to push it onto the front of your <code>[list]</code>. <code>:</code> is used to push some <code>a</code> onto the front of a list of <code>as</code> Like so:</p> <pre><code>Set (numberToInsert:[list]) </code></pre> <p>Finished product:</p> <pre><code>insert :: Int -&gt; Collection -&gt; Collection insert numberToInsert (Set [list]) | contains (Set [list]) numberToInsert == True = (Set [list]) | otherwise = Set (numberToInsert : [list]) </code></pre> <p><strong>Update</strong></p> <p>As you mentioned, there is one other issue I'd missed. <code>list</code> shouldn't be wrapped in the square brackets, and here's why (in case you hadn't figured it out).</p> <p>When you use the square brackets in a pattern match (the left side of the <code>=</code>), you're saying: "give me a list that looks like this, and bind it's only item to some name for use later". So you were only expecting a list with one item, and decided to call that item <code>list</code>.</p> <p>Next, you repackaged up that one item in the new list when you used it as <code>[list]</code>.</p> <p>this example:</p> <pre><code>foo [a] = a main = print $ foo [1] </code></pre> <p>would print '1'. Passing a list of two items, however, would fail to pattern match, because you had no <code>foo [a, b] = ...</code> function defined, hence the warning:</p> <pre><code>main = print $ foo [1, 2] </code></pre> <p>So yes, removing all of the square brackets works because you are not requiring the list have only one item, but instead saying "the entire list will be called <code>list</code>", which is probably what you wanted in the first place.</p>
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    1. COI get the error non-exhaustive pattern matching, when I put the brackets around list, but when i remove the brackets it works.
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    2. CONevermind I see the error
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    3. COOops, sorry about that. If you hadn't figured out why, see my update. I hope that helps.
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