Re: Rather simple function returns curious result.

*To*: mathgroup at smc.vnet.net*Subject*: [mg131409] Re: Rather simple function returns curious result.*From*: James Stein <mathgroup at stein.org>*Date*: Wed, 3 Jul 2013 05:02:46 -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> <51D26ADF.5080802@tue.nl>

Dear Fred, Thanks to you, and any others who respond. Another case of proof-reader's blindness when proof-reader and author are the same person. I had indeed meant to write ___List, not List___, and knowing what I meant, could not see what I wrote. Chagrined, James On Mon, Jul 1, 2013 at 10:53 PM, Fred Simons <f.h.simons at tue.nl> wrote: > 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>