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Re: [Scheme-reports] Seeking review of sets and hash tables proposals

"Procedure properties" can be implemented using an eqv? hash table,
provided eqv? is specified to work on procedures.  I find this fact
funny in this context, both because of the recent angst about eqv?
operating on procedures in R7RS (that I was part of), and because such
an implementation strategy for hash functions is not actually
circular, since the proper hash function for eqv? itself can be
supplied by other means.


On Sat, May 25, 2013 at 3:04 PM, Per Bothner <per@x> wrote:
> On 05/25/2013 09:45 AM, Per Bothner wrote:
>> A 'comparator' data type might be still be worth considering.
>> I could work well with a small library of utility routines.
>> For example (ascending PROJ) and (descending PROJ) take a one-argument
>> "projection" function that is applied to the elements to be
>> compared.  Another useful utility (useful for sorting)
>> takes a list of comparators, where the first element is
>> the primary key, the second the secondary key, etc.
>> Anyway, this is all very hand-wavy ...
> Another idea, focusing for now just on equivalance functions:
> If the language supports 'procedure properties' then one
> way to "bundle" an equivalance function with a hash function
> is to make the latter a property of the former.  For example,
> using Kawa's syntax:
> http://www.gnu.org/software/kawa/Procedure-properties.html
> One could define:
> (define-procedure my-eq?
>     equivalence-hash: (lambda (obj) (whatever-hash ... obj))
>     (lambda (obj1 obj2) (whatever-eq ... obj1 obj2))
> Then as user can do:
>    (make-hash-table my-eq?)
> and the implementation can extract the hash function as:
>    (procedure-property equivalence 'equivalence-hash)
> --
>         --Per Bothner
> per@x   http://per.bothner.com/
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