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MathGroup Archive 2005

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Returning an empty sequence

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63273] Returning an empty sequence
  • From: "Trevor Baca" <trevorbaca at gmail.com>
  • Date: Thu, 22 Dec 2005 00:04:34 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

What's the right way to have an expression evaluate to an empty
sequence?

I'd like ...

f[n_] :=
  Switch[n,
    1, "foo",
    2, Sequence[ ],
    3, {"bar"}];

... to work, but instead I get the message

Switch::"argct": "Switch called with 6 arguments. Switch must be called
with an odd number of arguments."

meaning that the Sequence[ ] is flattened in the rhs definition of f[
].

Is there a way to get f[ ] to evaluate to the empty Sequence[ ] (rather
than Null)?

Trevor.


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