[racket-dev] set operations

I've written a version of `set-choose', and also `set-first' and 
`set-rest' (with the obvious meanings) a few times. They can be useful.

(I always waffled about whether to use just `set-choose', or `set-first' 
along with `set-rest'. Mathematically, `set-first' and `set-rest' don't 
make sense, but they're easier to code with.)

Neil T

Ryan Culpepper wrote:
> I think a function named set-choose should return just the chosen 
> element. I would call the function below set-split, maybe.
> 
> Also, beware that for/first returns #f if the sequence is empty.
> 
> Ryan
> 
> On 11/11/2010 01:38 PM, Jay McCarthy wrote:
>> I think it is a good idea. Any objectors?
>>
>> Jay
>>
>> On Wed, Nov 10, 2010 at 12:40 PM, David Van 
>> Horn<dvanhorn at ccs.neu.edu>  wrote:
>>> The set library is missing a convenient way of selecting an element 
>>> from a
>>> set, making it hard to write recursive functions matching the inductive
>>> structure of a set.
>>>
>>> Could you add this function, or something like it?
>>>
>>> (define (set-choose s)
>>>   (let ((x (for/first ([x (in-set s)])
>>>              x)))
>>>     (values x (set-remove s x))))
>>>
>>> David
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>>
>>
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