Re: MakeExpression problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg77173] Re: MakeExpression problem*From*: Hannes Kessler <HannesKessler at hushmail.com>*Date*: Tue, 5 Jun 2007 06:41:32 -0400 (EDT)*References*: <200706031013.GAA02923@smc.vnet.net><f40g34$5uk$1@smc.vnet.net>

On 4 Jun., 09:47, "Chris Chiasson" <c... at chiasson.name> wrote: > 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 <HannesKess... 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/- Zitierten Text ausblenden - > > - Zitierten Text anzeigen - Thank you Chris, I think this solves my problem.

**References**:**MakeExpression problem***From:*Hannes Kessler <HannesKessler@hushmail.com>