</p><div class="doc"><p>Expr represents a user defined expression, 
 which consists of a description for comparisons and an evaluation function.</p></div><div class="subs constructors"><p class="caption">Constructors</p><table><tr><td class="src"><a id="v:Expr" class="def">Expr</a></td><td class="doc empty">&nbsp;</td></tr><tr><td colspan="2"><div class="subs fields"><p class="caption">Fields</p><ul><li><dfn class="src"><a id="v:desc" class="def">desc</a> :: <a href="Expr.html#t:Desc" title="Expr">Desc</a><