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Re: Using a logical Or in the function definition

• To: mathgroup at smc.vnet.net
• Subject: [mg86691] Re: Using a logical Or in the function definition
• From: Szabolcs Horvát <szhorvat at gmail.com>
• Date: Wed, 19 Mar 2008 05:20:30 -0500 (EST)
• Organization: University of Bergen
• References: <fro39q$i8a$1@smc.vnet.net>

ahallam at iastate.edu wrote:
> I would like to use Or in the function definition as in
> 
> ab[ Or[r_Integer,r_Rational], Or[s_Integer,s_Rational] ]:=r/s;
> 
> In other words, I want the function to take integers or ratios of
> integers as arguments, but not real numbers which are not rational.
> 
>  But if I give the function integer arguments, it does not evaluate.
> 
> If I try
> 
> ar[ r_Integer , Or[s_Integer , s_Rational]] := r/s;
> 
> and give an integer first argument it works and so on.
> 

Have you checked the documentation on how to construct patterns?

http://reference.wolfram.com/mathematica/guide/Patterns.html

You need Alternatives, not Or.

ab[ r:(_Integer|_Rational), s:(_Integer|_Rational) ]:=r/s

But perhaps you were looking for

ab[r_?ExactNumberQ, s_?ExactNumberQ] := r/s

?