Re: What to return on symbolic evaluation of own heads ?
- To: mathgroup@smc.vnet.net
- Subject: [mg12608] Re: [mg12511] What to return on symbolic evaluation of own heads ?
- From: "Jrgen Tischer" <jtischer@pitagoras.univalle.edu.co>
- Date: Mon, 25 May 1998 14:25:18 -0400
Hallo Andreas, MyCharFunc[left_, right_, var_?NumberQ]:=If[left<=var<=right,1,0] Jrgen -----Original Message----- From: Andreas Keese <a.keese@tu-bs.de> To: mathgroup@smc.vnet.net Subject: [mg12608] [mg12511] What to return on symbolic evaluation of own heads ? >Hi, > >I'm trying to build my own Datatype - as an example, I'll try to >construct a characteristic function. I define a characteristic function >like this: > >F[x_] := MyCharFunc[0,1,x] >(* this is the char func of the interval [0,1] *) > >And I try to define an evaluation-rule like this: > >MyCharFunc[left_, right_, var_]:= > If[NumberQ[var], > If[var < left || var > right, > 0, > 1], (* else - symbolic variable *) > MyCharFunc[left, right, var] > ] > >Of course, this doesn't work - while I can write F[0.5] and get a >correct result, I can't write F[x] as this results in an infinite >recursion --- but If I want to manipulate my data-object, I somehow >need to return the original object. E.G. I want to be able to write > F[x] /. x-> 3 >and have this evaluated as F[3]... > >What should I return in my evaluation-rule when the parameter is >symbolic ? > >Bye, >Andreas >