Re: Returning an empty sequence

*To*: mathgroup at smc.vnet.net*Subject*: [mg63290] Re: [mg63273] Returning an empty sequence*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 23 Dec 2005 05:08:17 -0500 (EST)*References*: <200512220504.AAA05673@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 22 Dec 2005, at 14:04, Trevor Baca wrote: > 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. > Yes. f[n_] := Switch[n, 1, "foo", 2, Unevaluated[ Sequence[ ]], 3, {"bar"}]; f[1] foo f[2] Sequence[] Andrzej Kozlowski

**References**:**Returning an empty sequence***From:*"Trevor Baca" <trevorbaca@gmail.com>