[racket-dev] Racket Questions?

From: David Van Horn (dvanhorn at ccs.neu.edu)
Date: Sat Sep 15 10:26:20 EDT 2012

On 9/14/12 3:36 PM, Becca MacKenzie wrote:
> Hello!
> So a friend of mine just started learning Racket and was wondering if
> there's a particular reason why the modulo function in racket only takes
> in integers? He wrote his own mod function to take in other things but
> he was just wondering what the reasoning is behind this.

Hi Becca,

Excellent question -- I hope you don't mind that I've forwarded it to 
the Racket developers list for a more authoritative answer (and 
potentially a change to Racket).

I don't believe there's any principled reason not to extend `modulo' to 
other kinds of numbers such as rationals and (exact) complex numbers.  I 
worry that the idea of modulo may not be well defined for inexact 
numbers, but I could be wrong (inexact numbers don't obey a lot of the 
usual mathematical properties we're used to).  I see that in 
Mathematica, "the arguments of Mod can be any numeric quantities, not 
necessarily integers".  Here are some examples:


Recently, Racket's GCD and LCM were extended to work on non-integer 
arguments, and I believe this is a similar case where the function could 
(and should?) be extended to work for more kinds of numbers.  But I'm 
interested to hear what the dev list has to say on the matter.


Posted on the dev mailing list.