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MathGroup Archive 2009

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Re: print variable name and its value

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99984] Re: print variable name and its value
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Thu, 21 May 2009 00:05:29 -0400 (EDT)
  • References: <gv0ius$b8v$1@smc.vnet.net>

Karsten W. wrote:
> Hello,
> 
> how can I dump out a variable with its value? The following does not
> work:
> 
> myVar1 = 1;
> myVar2 = 2;
> DumpVars[list_List] :=
>   MapThread[(Print[#1, ": ", #2]) &, {Map[ToString[#] &,
>      Unevaluated[list]], list}];
> 
> DumpVar[var_] := Print[ToString[Unevaluated[var]], ":", var];
> 
> 
> DumpVars[{myVar1, myVar2}]
> DumpVar[myVar1]
> 
> Any ideas?

Use attributes. To get ahold of the unevaluated forms within the
function definition you _need_ HoldFirst (or HoldAll). Listable just
makes the code simpler and probably can motivate you to learn more about
how attributes can make your life easier :-)

The following should do what you want:

ClearAll[DumpVar]

SetAttributes[DumpVar, {HoldFirst, Listable}]

DumpVar[s_Symbol] := (Print[HoldForm[s], ": ", s]);

Note that these both do work without further definitions, thanks to the
attribute Listable:

DumpVar[myVar1];

DumpVar[{myVar1, myVar2}];

hth,

albert


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