Reevaluation of conditional arguments when the condition has changed

*To*: mathgroup at smc.vnet.net*Subject*: [mg61046] Reevaluation of conditional arguments when the condition has changed*From*: "David Park" <djmp at earthlink.net>*Date*: Sat, 8 Oct 2005 02:49:21 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Dear MathGroup, Here is a programming problem that stumps me. We start with a condition that is always False. fooQ[_] := False Then write a definition that will factor out multipliers of fooQ objects. foo[a_ b_?fooQ] := a foo[b] The following does not factor because b, or anything else, fails the test. expr1 = foo[a b] giving: foo[a b] Now I define b as a fooQ object. fooQ[b] := True Now when I enter the same expression the a factors out. foo[a b] giving: a foo[b] But if I reevaluate expr1 the definition is not applied. expr1 giving: foo[a b] Why shouldn't I expect that to evaluate and now factor? Is there a proper way to write the definitions so it will evaluate? David Park djmp at earthlink.net http://home.earthlink.net/~djmp/

**Follow-Ups**:**Re: Reevaluation of conditional arguments when the condition has changed***From:*Igor Antonio <igora@wolf-ram.com>

**Re: Reevaluation of conditional arguments when the condition has changed***From:*Carl Woll <carlw@wolfram.com>

**Re: Reevaluation of conditional arguments when the condition has changed***From:*Chris Chiasson <chris.chiasson@gmail.com>