<p dir="ltr">Might be worth reading <a href="http://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-typeclass/">http://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-typeclass/</a></p>

<p dir="ltr">Especially in the context of guis and widgets.</p>
<p dir="ltr">Ben</p>