title: Very simple Haskell code doesn't work, "Variable not in scope"
body: <p>I'm new to Haskell and doing some simple exercises. For this exercise I'm writing a function that checks whether one list is a subset of another list using recursion.</p>
  
  <p>Here's the code:</p>
  
  <pre><code>subset [] xs = True
  
  subset (x:xs) ys = if elem x ys == False then False
                     else subset (tail xs) (delete x ys)
  </code></pre>
  
  <p>I'm getting the following error message:</p>
  
  <pre><code>C:\Functioneel programmeren\week4.hs:9:43: error:
      Variable not in scope: delete :: t1 -&gt; t t1 -&gt; t t1
  </code></pre>
  
  <p>What does this even mean?</p>
  
  <p>This program only works when I change "(delete x ys)" to "ys", but then it doesn't do what it's supposed to do.</p>
  
  <p>Any help would be great, thanks in advance.</p>