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MathGroup Archive 2002

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Optional

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33689] Optional
  • From: Ben Langton <ben at quickmath.com>
  • Date: Sat, 6 Apr 2002 00:49:16 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi all,

I am having a problem with the Optional function which I have reduced to the
following snippet of code :

f // Clear;
f[Optional[index : {_Integer ...}, {1}]] := index;
f[]

My understanding of the Optional command is that the function f should
accept a list of zero or more integers as its argument or, if that is
missing, use the default value of {1}.

Under version 3, f[] (f with no arguments) returns {1}, as I would expect,
yet under version 4.1 it returns the function evaluated.

Can anyone shed any light on why this code acts differently under the two
different versions? What can I do to make it work as expected under version
4.1?

Many thanks,

Ben Langton


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