Re: Re: MakeExpression problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg77167] Re: [mg77110] Re: [mg77095] MakeExpression problem*From*: DrMajorBob <drmajorbob at bigfoot.com>*Date*: Tue, 5 Jun 2007 06:38:25 -0400 (EDT)*References*: <200706031013.GAA02923@smc.vnet.net> <20534386.1180947138240.JavaMail.root@m35>*Reply-to*: drmajorbob at bigfoot.com

For instance: DoubleLongRightArrow[a_, b_] := Rule[a, b] a==>b a -> b (The second input line is entered as a Esc==>Esc b. Bobby On Mon, 04 Jun 2007 02:45:02 -0500, Chris Chiasson <chris 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 <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 >> >> >> > > -- DrMajorBob at bigfoot.com

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