# [plt-scheme] Is there a set data-type?

On Fri, Feb 05, 2010 at 03:54:13PM +0000, Paulo J. Matos wrote:
>* David Van Horn wrote:
*>* >
*>* >Uh, how do you represent the set of all even numbers, for example?
*>* >
*>* >This is an exercise we give our first semester undergraduates here at
*>* >Northeastern. I'll give you a hint: you don't need lists or hash
*>* >tables, go back to the mathematical foundations and think characteristic
*>* >functions.
*>* >
*>* >Now you do union, intersection, setminus, etc.
*>* >
*>*
*>* Good example... in fact, I didn't even thought about it when I
*>* implemented this... ahah Funny. Thanks for the counterexample.
*>*
*>* I guess the characteristic function approach involves using lambdas to
*>* represent a set... :-/ I am worried with efficiency but I will give it a
*>* try.
*
To do sets properly, you'd want the be able to enumerate the elements as
well as have a characteristic function. That can be done, of course,
for enumerable sets, anyway.
-- hendrik
>*
*>* >David
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