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Re: [Scheme-reports] Seeking review of sets and hash tables proposals
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:
One could define:
equivalence-hash: (lambda (obj) (whatever-hash ... obj))
(lambda (obj1 obj2) (whatever-eq ... obj1 obj2))
Then as user can do:
and the implementation can extract the hash function as:
(procedure-property equivalence 'equivalence-hash)
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