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Evaluate part of rhs of RuleDelayed

• To: mathgroup at smc.vnet.net
• Subject: [mg91081] Evaluate part of rhs of RuleDelayed
• From: "Eugene Kirpichov" <ekirpichov at gmail.com>
• Date: Tue, 5 Aug 2008 06:28:03 -0400 (EDT)

I am writing a lazy recursive function (actually, a tree of UI widgets
that is too large to be constructed at once).
Consider, for example, the following code:

SomeComplexFunction[a_] := Module[{x},
  x = a*a;
  {value :> SomeComplexFunction[x + a]}]

The value of SomeComplexFunction[5] is {value :>
SomeComplexFunction[x$7418 + 5]} and seemingly can'd be used for
anything useful.

Question:
How should I fix the code of SomeComplexFunction so that the value of
SomeComplexFunction[5] be {value :> SomeComplexFunction[30]} ?

Unfortunately, this one

SomeComplexFunction[a_] := Module[{x},
  x = a*a;
  {value :> SomeComplexFunction[Evaluate[x + a]]}]

yields {value :> SomeComplexFunction[Evaluate[x$7421 + 5]]}

-- 
Eugene Kirpichov
Web IR developer, Yandex

• Follow-Ups:
  • Re: Evaluate part of rhs of RuleDelayed
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Evaluate part of rhs of RuleDelayed
    • From: Carl Woll <carlw@wolfram.com>