Hey David,<br><br>For instance:<br><br><blockquote style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex; font-family: courier new,monospace;" class="gmail_quote">arity :: (Data a) => a -> Int<br>
arity = length . gmapQ (const ())<br></blockquote><br><br>Cheers,<br>Pedro<br><br><div class="gmail_quote">On Thu, Jun 25, 2009 at 17:31, David Fox <span dir="ltr"><<a href="mailto:ddssff@gmail.com">ddssff@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Is it possible to determine the arity of a value's constructor?<br>Suppose I have a value x of type<br>
<br> data A = B Int | C<br><br>They typeOf function returns its TypeRep, which contains its type<br>constructor, but I don't see how to decide whether that<br>
constructor's arity is 0 or 1. If the type has field names<br>I can look at those using Data.Data.conFields and count them,<br>but if it doesn't I don't see how to do it.<br><font color="#888888"><br>-david<br>
<br>
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