Re: MakeExpression problem
- To: mathgroup at smc.vnet.net
- Subject: [mg77110] Re: [mg77095] MakeExpression problem
- From: "Chris Chiasson" <chris at chiasson.name>
- Date: Mon, 4 Jun 2007 03:45:02 -0400 (EDT)
- References: <200706031013.GAA02923@smc.vnet.net>
Warning: I do not fully understand how operators are defined in
Mathematica, however I have some idea.
AFAIK, a MakeExpression rule is useless in a non-notebook environment
because the commands are (then) not represented as boxes.
You do not have to catch the DoubleLongRightArrow operator at the
"parsing" stage. Once
a==>b is read into Mathematica, it becomes the following expression (AFAIK):
DoubleLongRightArrow[a,b]
You can easily define a DownValue for DoubleLongRightArrow to do what you want.
This method should work for both notebooks and package files.
On 6/3/07, Hannes Kessler <HannesKessler at hushmail.com> wrote:
> Hello,
>
> here is a small package defining and using a generic MakeExpression
> interpretation rule:
>
> BeginPackage["DoubleLongRightArrow`"];
> {test1,test2,a,b,interpretation};
> Begin["`Private`"];
> MakeExpression[RowBox[{x_,"\[DoubleLongRightArrow]",y_}],form_]:=
> MakeExpression[RowBox[{"interpretation"}],form];
> test1=a\[DoubleLongRightArrow]b;
> (*The following assigment forces an interpretation by additional
> application of //ToBoxes//ToExpression*)
> test2=a\[DoubleLongRightArrow]b//ToBoxes//ToExpression;
> End[];
> EndPackage[];
>
> Here is a small notebook which calls the package.
> The typesetted \[DoubleLongRightArrow] looks in the notebook like ==>.
>
> Needs["DoubleLongRightArrow`"];
> (*The following expression is correctly interpreted in the notebook:*)
> In[] a==>b
> Out[] interpretation
> (*The expression read in the package is not interpreted:*)
> In[] test1
> Out[] a==>b
> (*Only the second expression converted first to boxes and then again
> to an expression is interpreted correctly*)
> In[] test2
> Out[] interpretation
>
> My question is, how can I define an interpretation rule in a package
> and use it in the same or other packages, not only in notebooks?
>
> Regards,
> Hannes Kessler
>
>
>
--
http://chris.chiasson.name/
- References:
- MakeExpression problem
- From: Hannes Kessler <HannesKessler@hushmail.com>
- MakeExpression problem