From Newsgroup: comp.lang.java.programmer


We are currently in our third iteration of
unification for rational trees. What first
begun as a separate routine inside library(math),
has now recently become a novel take on the
host language routine unify() inside the
Dogelog Player Prolog system.

We report how we replaced the union find map
data structure inside unify() by some Prolog
compound pointer swizzling as suggested by Jaxon
Jaffar in 1984, arriving at a more competetive
rational tree unification realization.

Jaxon Jaffar (1984) already proposed Hydra test
cases. They take very less memory but are very
large when written. We conducted according tests
with Dogelog Player and Scryer Prolog. For
N = 16'384, 65'536, 261'144 the Rust Prolog

has a minor advantage over the JavaScript Prolog,
but interestingly losing it for N = 1'048'576.

See also:

Jaffar's Unification in Dogelog Player https://qiita.com/j4n_bur53/items/b0b754f02d88680d3249

Mild Shock schrieb:

Dear All,

We are happy to announce a new edition
of the Dogelog Player:

- Frozen Terms:
We extended our garbage collector marking bits
to Prolog compounds. Unlike Prolog variables, where
setting all bits is used to indicate change set
membership, we use it to indicate frozen objects.
This makes the garbage collector and certain
built-ins such as copy_term/2 etc.. aware of
program sharing (PS).

- Marking Algorithms:
We now provide native implementations of (==)/2,
copy_term/2, etc.. with sharing and cycle detection.
We didn't deploy additional marking bits and/or
pointers inside the Prolog terms, instead used
additional datastructures, leaving the Prolog terms
untouched. The compare/3 implementation is
not a total order.

- Canonical Compare:
The library(lists) has experimental predicates
term_decompose/3 and term_canonical/2, still written
in 100% Prolog. We showcase their usage in
library(sequence) and library(aggregate). The end-
user gets by default a structure compare, but can
also have a canonical compare, both being
total and natural orders.

Have Fun!

Jan Burse, http://www.herbrand.ai/ , 21.08.2025

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