title: Function returns string when bool is expected
body: <p>What's wrong with this piece of code?</p>
  
  <p><code>fun expd s:string = if size(s) &gt; 0 then true else false;</code>
  <br></p>
  
  <p>The error I recieve:</p>
  
  <pre><code>- fun exnd s:string = if size(s) &gt; a then true else false;
  stdIn:657.1-837.8 Error: unbound variable or constructor: a
  Error: right-hand-side of clause doesn't agree with function result type [tycon mismatch]
    expression:  bool
    result type: string
  </code></pre>
  
  <p>Why is this happening?</p>