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MathGroup Archive 1996

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Dirty trick or legitimate style?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4036] Dirty trick or legitimate style?
  • From: hagai at helix.nih.gov (Hagai Agmon-Snir)
  • Date: Tue, 28 May 1996 01:45:51 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hi, Mathematica experts,

I am improving a package that I wrote a while ago. One of the things I
wanted to add is a function that gets an "operator" (practically, a
Mathematica expression), and performs this operation on the internal tree
structure (that is a part of the Private context of the package). I pass
the operator as a string and use ToExpression to calculate it in the
function (any better ideas?). Problem: the operator will not be calculated
in the correct "Private" context.

I solve this problem by the following "dirty" trick, that seems to work
fine - but ignores the style of Mathematica programming (I think). I
enclose just a tiny portion of the package - but the definition of
EvaluateCommand demonstrate the trick and  GeneralTransform shows an
example of actual use.

I am far from being a Mathematica expert, not speaking of package-writing.
If you have any better idea or if you think it is OK with the "Mathematica
code of style" - please let me know. You might also see "real" problems
with this trick (that are worse than the stylistic one).


BeginPackage["MET`",
 {"Graphics`Legend`","Graphics`Colors`"}];

EvaluateCommand::usage = " ";
GeneralTransform::usage = " ";

Begin["`Private`"];

EvaluateCommand[stringarg_]:=Module[{tmp},(
BeginPackage["MET`",
 {"Graphics`Legend`","Graphics`Colors`"}];
Begin["`Private`"];
tmp=ToExpression[stringarg];
End[];
EndPackage[];
tmp
)]

GeneralTransform[lroot_,stringarg_]:=
Module[{tmp},(
 BeginPackage["MET`",
  {"Graphics`Legend`","Graphics`Colors`"}];
 Begin["`Private`"];
 tmp=ToExpression[stringarg];
 tmp=Evaluate[tmp]&;
 PassTreeRecursive[lroot,
    ((#[Strl]=(N[tmp[#]]))&)
 ];
 End[];
 EndPackage[];
)];


PassTreeRecursive[lroot_,lfunc_] := (
 Apply[lfunc,List[lroot]];
 If[Length[lroot[Schildren]] >0 ,
  Map[PassTreeRecursive[#,lfunc]&,lroot[Schildren]]];
 );

End[];

EndPackage[];


Yours,

Hagai Agmon-Snir

>>>>>>>>>>>>>>>>>>  ================================  <<<<<<<<<<<<<<<<<
Hagai Agmon-Snir                                    Tel: (301) 496-9972
                                                         (301) 496-4325
Surface mail:                                       Fax: (301) 402-0535
 Mathematical Research Branch, NIDDK
 9190 Rockville Pike - Suite 350
 Bethesda, MD 20814-3800
 USA

E-mail: hagai at helix.nih.gov         WWW: http://mrb.niddk.nih.gov/hagai
<<<<<<<<<<<<<<<<<  ================================  >>>>>>>>>>>>>>>>>>



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