On 23.06.2023 00:45, Philip McGrath wrote: > On Thursday, June 22, 2023 7:33:06 AM EDT Taylan Kammer wrote: >> On 22.06.2023 00:25, Philip McGrath wrote: >>> Hi, >>> >>> What is the recommended way for a library to customize `equal?` and >>> `equal?` -based hashing for new datatypes it defines? >>> >>> I know from [1] that `equal?` can be customized using GOOPS; however, some >>> projects do not use GOOPS (e.g. [2]), so it would seem more friendly for a >>> generic library to avoid it. Also, it is not clear if the same mechanism >>> is >>> even an option for customizing `equal-hash` to match `equal?`. >>> >>> I'm looking for something like Racket's `gen:equal+hash` [3] or Chez >>> Scheme's `record-equal-procedure` and `record-hash-procedure` [4]. >>> >>> This came up while I was working on a portable version of the immutable >>> hash-table implementations from Racket-on-Chez. >>> >>> -Philip >>> >>> [1]: >>> https://www.gnu.org/software/guile/manual/html_node/GOOPS-Object-Miscella >>> ny.html [2]: >>> https://lists.gnu.org/archive/html/info-gnu/2023-05/msg00005.html [3]: >>> https://docs.racket-lang.org/reference/Equality.html#%28part._.Implementi >>> ng_.Equality_for_.Custom_.Types%29 [4]: >>> https://cisco.github.io/ChezScheme/csug9.5/objects.html#./objects:h14 >> Hi Philip, >> >> You can use SRFI 69 hash tables in Guile. This library offers a way to >> specify the equality and hash procedures that should be used by a hash >> table, e.g.: >> >> [...] >> >> Note that this doesn't affect the behavior of the standard 'equal?' >> procedure, it only affects the SRFI 69 hash table operations on the created >> hash table. >> >> I currently don't remember whether Guile's own non-portable hash table >> library supports the same feature. It probably does in some way. >> > > Thanks, but this is the opposite of what I want to do. The library I'm > porting > already supports creating tables with custom equality and hashing functions. > What I'm trying to do is make the standard `equal?` procedure recognize when > two of my table values are semantically the same even if internal > implementation details differ. > > (Note also that SRFI 69 and other libraries provide *mutable* hash tables. > The > Racket-on-Chez library I'm porting provides immutable hash tables, more > properly Hash Array Mapped Tries, as made famous by Clojure.) > > -Philip
Ah, apologies then. As far as I know, there's no other way to do that in Guile than with GOOPS, which you've already mentioned. In standard Scheme there's no way to do it at all. I don't think there's even an SRFI for it (I just searched a bit, out of curiosity, couldn't find anything). -- Taylan
