Re: Rather simple function returns curious result. Explanation
- To: mathgroup at smc.vnet.net
- Subject: [mg131387] Re: Rather simple function returns curious result. Explanation
- From: Fred Simons <f.h.simons at tue.nl>
- Date: Wed, 3 Jul 2013 04:55:25 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- Delivered-to: l-mathgroup@wolfram.com
- Delivered-to: mathgroup-outx@smc.vnet.net
- Delivered-to: mathgroup-newsendx@smc.vnet.net
- References: <20130702044842.DB5BC6A5F@smc.vnet.net>
Hi James,
The problem is in List___. In this way, you use the Mathematica name
List as a dummy name for passing the arguments into the function body.
If you use the correct syntax ___List (any number of arguments, all with
head List), the problem is over.
Regards,
Fred Simons
Eindhoven University of Technology
Op 2-7-2013 6:48, James Stein schreef:
> For reasons that escape me, the simple function below fails to return
> an empty List when n==2; Is this a bug? If not, what is the
> explanation? If the return value for n==2 is changed to an integer or
> a string, the function behaves as expected.(Of course, this bizarre
> function is the result of simplifying a more reasonable one.)
>
> Clear[ f ];
> f [run : { List___ } ] := Module [ { n },
> n = run // Length;
> If [ n != 2, Return [ n ] ];
> Module [ { } ,
> { } (* Return Empty List if n==2 *)
> ]
> ] ;
> f [ { } ]
> f [ { { } } ]
> f [ { { }, { } } ]
> f [ { { }, { }, { } } ]
> f [ { { }, { }, { }, { } } ]
>
> When I run the above, I get these four outputs:
> 0
> 1
> Sequence[{}, {}][]
> 3
> 4
>
>
- References:
- Rather simple function returns curious result. Explanation requested.
- From: James Stein <mathgroup@stein.org>
- Rather simple function returns curious result. Explanation requested.