Scheme Request for Implementation 161,
"Unifiable Boxes,"
by Marc Nieper-Wißkirchen,
has gone into "final" status.

The document and an archive of the discussion are available at
<https://srfi.schemers.org/srfi-161/>.

Here's the abstract:

  Unifiable boxes are, like the boxes of SRFI 111, objects with a
  single mutable state.  A constructor, predicate, accessor, and
  mutator are provided.

  In addition to this, an equality predicate and union operations
  (link, union, unify) are provided.  Applying a union operation
  to two unifiable boxes makes the two boxes equal (in the sense
  of the equality predicate).  As a consequence, their state will
  also become identical.  In the case of link and union, it will
  be the state of one of the two unioned boxes.  In the case of
  unify, the state is determined by a supplied unification
  procedure.

  Unifiable boxes are also known under the names disjoint-set data
  structure, union–find data structure or merge–find set.

Many thanks to Marc and to everyone who contributed to the
discussion of this SRFI.

Regards,

SRFI Editor