Most of the changes since the last full release (3.1) are provided in
the release notes of 3.1a and 3.1b.

The most significant changes since release 3.1b are as follows:

	a)	A settings tool can be opened from the SDML launcher
(from the "File" menu). This tool has several pages, each of which
has a "Help" button describing the options. The most important page
is labelled "Memory" - these settings can make a big difference to
the efficiency of SDML.

	b)	Lists of bugs plus bug fixes and enhancements were
available for earlier releases of SDML were obtainable as two
separate files - one containing text descriptions and the other
containing additional information, including the patches to SDML
themselves. These are now combined into a single "patches file",
called "sdml3-2.pat". The file also contains some additional
information - dates and times, plus distributions (details of which
releases of SDML that the bugs and patches are applicable to, and
whether they are "local"). Patches can now be developed for multiple
releases of SDML simultaneously, and some of them may initially be
"local" enabling them to be tested at the Centre for Policy Modelling
before distributing them to other users.

	c)	A "bug report" generation facility is provided, to
make it easier to report bugs in SDML so that (hopefully) I, Steve
Wallis, can solve them. The bug reports can be generated via the
notifiers that appear when Smalltalk errors occur outside simulations
or experimentations - or from a menu option in the top pane of the
debugger.

	d)	A new "constructedList" higher-order primitive is
provided, which repeatedly evaluates another predicate to yield
elements of a new list.

	e)	A new "if" primitive is provided, which is similar to
"if-then-else" in other languages.

	f)	An additional menu, labelled "Window", is added to
the SDML launcher and workspace browser. The menu options can be used
to refresh, collapse or restore all windows on the screen - or to
make a specific window visible.

	g)	Every backward chaining rule in a clause definition's
rulebase must have a single consequent with the appropriate
predicate. This is enforced by initialising the consequents to that
predicate (with no arguments), checking for the predicate when the
user edits the rule, and changing the consequent when the user copies
the rule.

	h)	Inverse operations, which are created when an
operation is undone without being redone, are shown in italics in the
operation list. [The inverse of an inverse is the original operation,
so it is shown in the normal font.] This makes it easier to determine
which operations need to be performed to return SDML to a particular
state. Additionally, representing inverses in the operation list
facilitates optimisation when multiple operations are performed at
once.

	i)	Type "UniversalAgent" is now a subtype of
"CompositeAgent" rather than "ParallelCompositeAgent", and the
universe can only have one sub-agent (typically the model). [If
multiple models are required within the same simulation, this can
still be done by making the models sub-agents of the single sub-agent
of the universe; in practice this was necessary anyway in earlier
releases since the universe cannot use any time levels apart from
eternity.]

It should be noted that two of the features introduced in release
3.1a still have not been fully implemented. The user interface
extensions are planned to change drastically in the (fairly) near
future so users are strongly discouraged from using them. The "sole"
facility is only implemented for forward chaining predicates where
all the arguments are defined as "sole"; it can be used for arguments
in other clause definitions but no optimisation or type checking will
be performed for them.