[plt-dev] scheme/set

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Tue Feb 23 10:32:06 EST 2010

Thanks for adding the set library. I am looking forward to using these  
in *SL.

On Feb 23, 2010, at 9:16 AM, Matthew Flatt wrote:

> I don't see how it's a problem to add new constructors in the future
> and to liberalize the contracts on the `set' functions for those  
> future
> variants. I'll readily concede, however, to anyone who wants to do the
> work of improving the current first cut.
> At Tue, 23 Feb 2010 08:53:18 -0500, Sam Tobin-Hochstadt wrote:
>> On Tue, Feb 23, 2010 at 8:35 AM, Matthew Flatt <mflatt at cs.utah.edu>  
>> wrote:
>>> At Mon, 22 Feb 2010 20:39:54 -0500, Carl Eastlund wrote:
>>>> I appreciate the addition of sets to PLT datatypes, but the
>>>> implementation just added to the trunk is very specific to  
>>>> immutable,
>>>> hash table-based sets.  In the spirit of scheme/dict, which  
>>>> allows for
>>>> a variety of more interesting dictionary representations, can we  
>>>> leave
>>>> scheme/set open to other representations of sets?
>>> Does something in the current `scheme/set' API preclude future
>>> extensibility (e.g., adding `prop:set')?
>> The following aspects of `scheme/set' seem designed-in to the  
>> current API:
>> - that elements must not be mutated (even if there were other
>> implementations, the fact that the primary one has this restriction
>> means that it's not safe)
>> - the three comparison functions are written in to the API, rather
>> than being extensible (which would be hard to change given the  
>> current
>> implementation, since those are the hash functions that are allowed)
>> One nice way to improve this would be to have a concept of 'hash
>> sets', where (hash-set? s) implies (set? s).  That leaves open the
>> door to equality based or comparison based sets in the future.   
>> Almost
>> all of the API would stay the same, but the constructors and
>> predicates would change.
>> -- 
>> sam th
>> samth at ccs.neu.edu
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