Re: about scoping in modules
- To: mathgroup at smc.vnet.net
- Subject: [mg85913] Re: about scoping in modules
- From: Oliver Ruebenkoenig <ruebenko at uni-freiburg.de>
- Date: Wed, 27 Feb 2008 04:32:24 -0500 (EST)
- References: <fpkvqk$hrr$1@smc.vnet.net> <fpmeur$8em$1@smc.vnet.net>
On Tue, 26 Feb 2008, David Bailey wrote:
> Oliver Ruebenkoenig wrote:
>> On Fri, 22 Feb 2008, David Bailey wrote:
>>
>>> P_ter wrote:
>>>> Hello,
>>>> in the next two modules I would like that the inner module uses a variable from the outer module.
>>>> mfb[oneObj_] := Module[{ttmp = oneObj},AppendTo[ global2mfb, ttmp]]
>>>> mfa[e_] := Module[{global2mfb = e, t = 3},mfb[t] ]
>>>> mfa[{2,3}] gives a message that global2mfb is not a variable with a value, so it can not be changed.
>>>> It means I do not understand the concept of module in Mathematica. My questions are:
>>>> 1. why does it go wrong?
>>>> 2. how can I realize what I want?
>>>> with friendly greetings,
>>>> P_ter
>>>>
>>> Well, despite its name, global2mfb is local to the Module in which it
>>> appears - so using it elsewhere refers to a global variable of the same
>>> name with no value - hence the diagnostic. This is the purpose of Module
>>> - to stop one use of a variable clashing with another.
>>>
>>> Take the assignment global2mfb=e outside the list of local
>>> initialisations, and I think you will get what you want.
>>>
>>
>> almost,
>>
>> AppendTo needs a reference not an explicit List
>>
>> such as
>>
>> x={1,2}
>> AppendTo[x,1]
>>
>> AppendTo[{1,2},3] can not work since:
>> Attributes[ AppendTo]
>>
>> you could not access the result.
>>
>> Oliver
>>
>> Oliver Ruebenkoenig, <ruebenko AT uni-freiburg.de>
>>
> Sorry, I don't know what you mean. Here is the original code modified as
> I suggested:
>
> In[86]:= mfb[oneObj_]:=Module[{ttmp=oneObj},AppendTo[global2mfb,ttmp]];
> mfa[e_]:=Module[{t=3},
> global2mfb=e;
> mfb[t]]
> In[88]:= mfa[{2,3}]
> Out[88]= {2,3,3}
>
> AppendTo is operating on a variable (or reference, if you prefer)!
>
> David Bailey
> http://www.dbaileyconsultancy.co.uk
>
>
Sorry, David, you are right. I do not know what I was thinking - probably
not at all :-(
Oliver
Oliver Ruebenkoenig, <ruebenko AT uni-freiburg.de>