🚀 go-pugleaf

OK, here's another shot at a problem that seems to call for GC; let's see
what y'all can make of it.

One of the elements of the Prolog language is the "atom" (read "name" or
"symbol").  In the language model, atoms aren't created or destroyed, they
just *are* (like the integers, for instance).  To support this model, the
Prolog interpreter must allocate a block in "atom space" whenever a mention
of a new atom is required (either read in or needed as the result of a
string-to-atom conversion).  Problem: when to delete blocks in atom space?
The Prolog user is no help, having no concept of "atom deletion".

Reference counting is one possibility, but it has one serious defect.
During backtracking, which is a common Prolog operation, potentially large
chunks of stack space are "cut away"; to have to wade through that space
finding pointers and decrementing counts would be a major performance hit.
IMHO, a good asynchronous garbage collector working in the background would
be the best solution.

Historical note: at the time I was last involved in implementations of
Prolog (several years ago), atom space was generally not "cleaned up" at
all; when it filled up, the system had to abort.

--
Don Dwiggins				"Solvitur Ambulando"
Ashton-Tate, Inc.
dwiggins@ashtate.uucp