Re: Symbols, names, objects: kludge
- To: mathgroup at smc.vnet.net
- Subject: [mg6548] Re: [mg6517] Symbols, names, objects: kludge
- From: David Withoff <withoff>
- Date: Mon, 31 Mar 1997 23:01:47 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
> In an earlier posting, I asked how to define a function
> store[varname_String, dataname_String] that causes a variable to be
> created whose name is given by the string used as first argument and
> which assigns as the value of that new variable the value of the
> object whose name is given by the string used as the second argument.
> For example,
>
> x = 99;
> store["myx", "x"]
>
> should mean that an input
>
> myx
>
> now produces
>
> 99
>
> as output.
>
> I found one method that works -- sort of, and sometimes -- but which I
> don't fully understand:
>
> store[varname_String, dataname_String] :=
> ToExpression[StringJoin[Sequence@@{varname,"=",dataname}]]
>
> Unfortunately, I need to use such a function store inside a Module,
> like this:
>
> wrapper[shortname_String] := Module[{temp},
> temp = ...... (* value created here *) ;
> store["new"<>shortname, "temp"];
> ....
> ]
>
> and now, because temp is a local variable in the Module, the whole
> thing breaks down (assigning the SYMBOL temp as the value of the
> new... variable).
>
> A real kludge is:
>
> wrapperkludged[shortname_String] :=
> (temp = ...... ;
> store["new"<>shortname, "temp"];
> Remove[temp]
> )
>
> but clearly that is most unpleasant (since, in my actual application,
> there are a whole bunch of local variables in the Module that calls
> the function store.
>
> So I'm still seeking a satisfactory solution!
>
> --
> Murray Eisenberg Internet: murray at math.umass.edu
> Mathematics & Statistics Dept. Voice: 413-545-2859 (W)
> University of Massachusetts 413-549-1020 (H)
> Amherst, MA 01003 Fax: 413-545-1801
My best guess here that you should try Block rather than Module.
Block leaves the name of the symbol unchanged, so if you generate
a new symbol with that name, it will refer to the local symbol.
Module also localizes the name of the symbol, so if you generate
a new symbol during evaluation of the Module, that new symbol will
refer to something else.
Dave Withoff
Wolfram Research