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  • SRFI 250: Insertion-ordered hash tables

    From Arthur A. Gleckler@21:1/5 to All on Wed Nov 15 11:07:10 2023
    Scheme Request for Implementation 250,
    "Insertion-ordered hash tables",
    by John Cowan,
    is now available for discussion.

    Its draft and an archive of the ongoing discussion are available at <https://srfi.schemers.org/srfi-250/>.

    You can join the discussion of the draft by filling out the
    subscription form on that page.

    You can contribute a message to the discussion by sending it to <[email protected]>.

    Here's the abstract:

    This SRFI defines an interface to hash tables, which are widely
    recognized as a fundamental data structure for a wide variety of
    applications. A hash table is a data structure that:

    - Is disjoint from all other types.
    - Provides a mapping from objects known as keys to corresponding
    objects known as values.
    - Keys may be any Scheme objects in some kinds of hash tables, but
    are restricted in other kinds.
    - Values may be any Scheme objects.
    - Provides an equality predicate which defines when a proposed key
    is the same as an existing key. No table may contain more than one
    value for a given key.
    - Provides a hash function which maps a candidate key into a
    non-negative exact integer.
    - Supports mutation as the primary means of setting the contents of
    a table.
    - Provides key lookup and destructive update in (expected) amortized
    constant time, provided that a satisfactory hash function is
    available.
    - Does not guarantee that whole-table operations work in the
    presence of concurrent mutation of the whole hash table. (Values
    may be safely mutated.)
    - Unlike the hash tables of SRFI 125, which is the direct ancestor
    of this specification, the hash tables described here are ordered
    by insertion: that is, associations inserted earlier in the
    history of the hash table appear earlier in the ordering. Advances
    in the implementations of hash tables, as provided by C++, Python,
    JavaScript, etc., make the provision of this new facility
    practical. As a result, the hash tables of this SRFI do not
    interoperate with the hash tables of SRFI 125, SRFI 126, or
    existing R6RS implementations.

    Regards,


    SRFI Editor

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