Re: Validating functions input
- To: mathgroup at smc.vnet.net
- Subject: [mg58800] Re: Validating functions input
- From: David Bailey <dave at Remove_Thisdbailey.co.uk>
- Date: Tue, 19 Jul 2005 04:10:08 -0400 (EDT)
- References: <dbflkk$n0p$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Nilton wrote: > 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 > Hello, All you need to do is pick off the case that requires an error message and leave the others: f[x_,y_] := Message[f::invalid]/;x>2^y; David Bailey http://www.dbaileyconsultancy.co.uk