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Validating functions input

• To: mathgroup at smc.vnet.net
• Subject: [mg58784] Validating functions input
• From: "Nilton" <nilton.volpato at ig.com.br>
• Date: Mon, 18 Jul 2005 03:21:21 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

I have a function that must have its input validated.

f[x,y]

I want to validate if x <= 2^y. If it's valid, then just return the
symbol f[x,y] unevaluated. If it's not valid, I want to return some
symbol, Null for instance, and issue an error message.

The following is a try, but it doesn't work, because it's definition is
recursive:

f::invalid = "Invalid arguments"
f[x_,y_] := If[x <= 2^y, f[x,y], Message[f::invalid]]

Is there any way to implement this?

Thanks,
-- Nilton

• Follow-Ups:
  • Re: Validating functions input
    • From: Chris Chiasson <chris.chiasson@gmail.com>