On Dec 21, 2007 11:50 AM, Nicholls, Mark &lt;<a href="mailto:Nicholls.Mark@mtvne.com">Nicholls.Mark@mtvne.com</a>&gt; wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Now I have....<br><br>module Main where<br><br>data SquareType numberType = Num numberType =&gt; SquareConstructor<br>numberType</blockquote><div><br>This is a valid declaration, but I don&#39;t think it does what you want it to. The constraint on numberType applies only to the data constructor.
<br><br>That is, given an unknown value of type SquareType a for some a, we do not have enough information to infer Num a.<br><br>For your code, you want something like:<br><br>instance (Num a) =&gt; ShapeInterface (SquareType a) where
<br>&nbsp;&nbsp;&nbsp; area (SquareConstructor side) = side * side<br></div></div><br>-- <br>Dave Menendez &lt;<a href="mailto:dave@zednenem.com">dave@zednenem.com</a>&gt;<br>&lt;<a href="http://www.eyrie.org/~zednenem/">http://www.eyrie.org/~zednenem/
</a>&gt;