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:

   http://reference.wolfram.com/mathematica/ref/Mod.html#6881

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.

David

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