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Prolog news for Poplog Version 14.0.

For more recent news, see HELP * PLOGNEWS.

1990 ==================================================================

October (Simon Nichols) ----------------------------------------------

--- The Prolog error printer has been changed to use print/1 to print
    culprits, thereby making use of any portray/1 clauses which have
    been defined.

--- The evaluable predicate functor/3 has been changed to fail if its
    third (arity) argument is a negative integer. Similarly, arg/3 now
    fails if its first argument is an integer which is negative or
    greater than the arity of the Term which is its second argument.
    Previously, both functor/3 and arg/3 raised errors in these cases.
    The new behaviour is more logically correct and is compatible with
    other major Prolog systems.

--- The evaluable predicate print/1 has been fixed so that it now tries
    portray/1 at each level of the term being printed. Previously, if
    the call to portray/1 failed at the top-level of the term, write/1
    was invoked immediately. See PLOGHELP * PRINT.

--- The names read/2 and write/2 have been made synonyms for vread/2 and
    vwrite/2, respectively, for compatibility with other Prolog systems.

--- The functionality of the evaluable predicate save/2 has been
    considerably enhanced. It now accepts as its second argument a
    (possibly empty) list of attributes, which give control over whether
    the Prolog saved image is created as a locked system (and if so
    whether the nonwriteable area should be made shareable) and whether
    standard Prolog system initialisation should be performed when the
    image is restored. See PLOGHELP * SAVE for details.

August (Simon Nichols) -----------------------------------------------

--- The evaluable predicate predicate_info/2 has been made more
    informative: it will now report on whether a predicate has been
    declared but not defined and also whether a user-defined predicated
    was defined in a language other than Prolog.
    See PLOGHELP * PREDICATE_INFO for details.

July (Simon Nichols) -------------------------------------------------

--- A new command, pop11, has been added which switches subsystem to
    POP-11. This is similar to the POP11 command defined by loading
    LIBRARY * LANGUAGES, but is available without having to load a

--- Commands (e.g. ved, help, teach, cd, etc.) are no longer macros.
    They have been re-implemented in such a way that they are
    recognised either:

        (1) at top-level, in place of a query;
        (2) in a file being (re)consulted, in place of a clause or

    The effect is that commands names may be freely used as atoms in
    terms, hopefully fixing a long-standing complaint.
    See PLOGHELP * COMMANDS for details.

April (Simon Nichols) ------------------------------------------------

--- A new facility has been added which allows the pre-processing of
    clauses read when consulting or reconsulting a file. The user may
    define transformations to be applied to each clause by asserting
    clauses for the predicate term_expansion/2.
    See PLOGHELP * EXPAND_TERM for details.

February (Simon Nichols) ---------------------------------------------

--- The new LIBRARY * EDINSYNT provides full Edinburgh (or DEC-10)
    syntax in POPLOG Prolog. To get full Edinburgh syntax, type:

        ?- library(edinsynt).

    followed by:

        ?- prolog_syntax(edinburgh).

    See PLOGHELP * EDINSYNT for details.

1989 ==================================================================

September (John Gibson) -----------------------------------------------

--- The system's handling of list structures in various contexts has
    been improved, by replacing recursive processing of list members with
    iterative processing. This means that certain programs using large
    lists will no longer require an increased -pop_callstack_lim- to
    allow them to run.

August (Robert Duncan) ------------------------------------------------

--- The module system has now been incorporated into the standard Prolog
    system rather than being a library. Library MODULES has been
    temporarily changed to print a warning when loaded, and will
    eventually be deleted. Improvements have been made to the modules in
    terms of error checking and reporting, and there are several new
    features defined:

        endmodule Name
            like 'endmodule/0', but unifies Name with the name of the
            current module;

            unifies Name with the name of the current module; fails if
            not in a module;

            unifies Name in turn with the name of each module
            currently defined;

            invokes Goal inside module Name;

            invokes Goal outside of any module.


--- Two new predicates 'vread/2' and 'vwrite/2' have been added. These
    behave like 'read/1' and 'write/1' except that the second argument
    is an environment associating variables with atomic names.

--- The method by which the standard Prolog saved image is built has
    been changed. Users who are familiar with the old method, i.e. with
    the files "mkplog" in $POPCOM and "prolog.p" in $USEPOP/pop/plog/src
    may like to look at the new versions of these to see what has

August (Andrew Casson) ------------------------------------------------

--- It is now possible to do

        X -> Y.

    instead of

        X -> Y ; fail.

    i.e. the "else" part of the conditional is optional.

March (Robert Duncan) -------------------------------------------------

--- The predicates 'setof/3' and 'bagof/3' have been modified to allow
    quantification over arbitrary terms. For example, the goal:

        bagof(X, (Y,Z)^p(X,Y,Z), S).

    is now equivalent to

        bagof(X, Y^Z^p(X,Y,Z), S).

    This can be useful where the set of bound variables has to be passed
    in as an argument.

--- LIBRARY * FINDALL has been rewritten in POP-11 so as not to use
    assert and retract; as a consequence it now runs *much* faster.

--- Expansion of grammar rules has been improved to allow meta-calls on
    the right-hand side of rules. For example, the rule:

        ident(X) --> X.

    now expands correctly, where previously it would cause the compiler
    to loop indefinitely. The meta-call expands to a call to phrase/3,
    and this has now been exported from the Prolog system.

1988 ==================================================================

September (Robert Duncan) ---------------------------------------------

Some minor improvements and fixes:

--- The default definition of prolog_error/2 has been simplified so that
    calls to unknown predicates now just fail, without having dummy
    clauses asserted for them as in the past. This gives more standard
    Prolog behaviour. A new option has been added to LIBRARY * UNKNOWN
    which re-establishes the old behaviour for those who want it. See

--- A new predicate prolog_abolish/2 has been introduced. This behaves
    like the standard abolish/2, except that it also works on system
    predicates. This makes it possible to redefine system predicates,
    although there are caveats -- see PLOGHELP * PROLOG_ABOLISH.

--- The VED command <ENTER> POPHELP, which accesses POP help files from
    Prolog, has been fixed.

--- The predicate prolog_evaltrue/1 has now been properly exported from
    section prolog and so can be called anywhere (it would previously
    work in some contexts but fail in others).

--- Operator declarations for the predicates dynamic/1, no_clauses/1,
    system_predicate/1 and their relatives have been added into
    LIBRARY * DEC10.

February (Robert Duncan and Simon Nichols) ----------------------------

--- New predicate declarations have been implemented. Predicates which
    are to be asserted and retracted can now be declared "dynamic". The
    global attributes "prolog_syspredicates" and "prolog_no_clauses" can
    now be applied on a per-predicate basis by means of the declarations
    "system_predicate" and "no_clauses". The predicate predicate_info/2
    gives information about how a particular predicate has been


--- The predicates see/1 and tell/1 have been modified so that they will
    accept a POP-11 character repeater (or consumer) as argument. This
    should simplify mixed-language programs which call Prolog from
    contexts in which input and output streams have been specially
    constructed (e.g in window-based applications). See PLOGHELP * I_O
    for details.

January (Robert Duncan and Simon Nichols) -----------------------------

--- Improvements have been made to the database handling mechanism. The
    predicates assert/1, retract/1 and clause/2 (and their derivatives)
    now all work substantially faster than previously. Certain
    inconsistencies in behaviour have also been removed.

--- Many of the frequently-used system predicates (such as functor/3,
    =../2 etc.) have been re-written and now run faster.

--- The error reporting mechanism has been changed. A wider range of
    error messages is now produced and the format has been smartened up.
    When errors arise from POP-11 procedures (for example, on the right
    hand side of an "is") their names now also appear in the backtrace
    in the DOING line of the error message.

--- The library POPSETQ has been withdrawn. The predicates defined in
    it, prolog_setq/2 and prolog_val/2, are now part of the system. For
    the time being, an empty library file "" has been kept so
    that existing calls to load the library will still succeed, but this
    will be removed in due course. See PLOGHELP * PROLOG_SETQ.

--- A new predicate float/1 has been introduced to complement the
    existing integer/1. See PLOGHELP * FLOAT.

--- A bug which allowed uninstantiated variables to be asserted and
    called has been fixed. This is now an error.

--- New documentation has been added:

1987 ==================================================================

Nov 10 (Simon Nichols)
    --- A bug whereby the operands to the relational operators </2,
    <=/2, >/2 and >=/2 were not always evaluated has been fixed. The
    symptom of this bug would have an error message such as:


Jul 1 (Robert Duncan)
    --- Please note that enhancements planned for POPLOG Prolog
    necessitate the withdrawal of the BASEPROLOG library from version 14

Jun 1  (Simon Nichols)
    --- A new VED command, <ENTER> POPHELP <topic> is now available from
    Prolog only. It looks for a POP11 HELP file on the specified topic,
    rather than looking first for a Prolog HELP file.

May 29 (Robert Duncan and Simon Nichols)
    --- The VED commands to mark and load the current procedure
    (<ENTER> MCP and <ENTER> LCP, usually bound to ESC-C) and to search
    for the start of a procedure definition (<ENTER> F) now work with
    Prolog. The MCP and LCP facilities interpret "procedure" as a
    sequence of clauses surrounding the current cursor position and
    having the same functor and arity. The <ENTER> F command will search
    either for a particular predicate, specified as name/arity, or for
    any predicate whose functor name has a given prefix.

May 29 (Robert Duncan and Simon Nichols)
    --- Some new macros have been made available from Prolog top-level:
        im  - to go into VED immediate mode
        pwd - to print the current directory
        cd  - to change directory

May  1 (John Williams)
    --- Some new facilities for mixed language programming have been
    added. These are:

        POP11 libraries:        LIB PLOG_GOALS     LIB PLOGINPOP
        Prolog libraries:       LISPINPLOG
        Lisp modules:           PROLOG

    the Lisp help file PROLOG.

Apr 23 (Robert Duncan and Simon Nichols)
    --- SPY has been changed to work correctly in conjunction with
    modules - SPY output is produced only for predicates visible in the
    current module. See PLOGHELP * MODULES, PLOGHELP * SPY.

Mar 15 (John Gibson)
    --- A further enhancement to V13 POPLOG Prolog means that compiled
    predicates containing large numbers of unit clauses will now occupy
    only a fraction of the space they previously occupied (on average,
    about one quarter). This should help considerably in reducing the
    memory load of the system.

Mar 6 (Simon Nichols)
    --- LIBRARY CHARTYPE has been created to allow character class
    numbers to be examined and changed from inside Prolog. See

Feb 26 (Robert Duncan and Simon Nichols)
    --- A new Prolog parser/itemiser has been implemented in Version 13.
    This fixes the known Prolog parsing bugs, particularly those
    concerned with the treatment of operators and punctuation
    characters, and provides better error reporting.

    The parser now differentiates correctly between "x" and "y"
    arguments in operator types so that, for example, an operator of
    type "xfx" is taken to be non-associative. Some operators have had
    their precedences changed accordingly, particularly the directive
    introducer "?-" and all those defined in LIBRARY MODULES, but this
    should not affect existing programs. [Note: some existing programs
    which rely on the previous, slacker, interpretation of operator
    types may no longer compile.] See PLOGHELP * OP for details.

    The parser now also forbids the use of the punctuation symbols "|"
    and "," as atoms unless quoted.

    A new HELP file, PLOGHELP * SYNTAX, describes the syntax of POPLOG

Feb 26 (Robert Duncan and Simon Nichols)
    --- Improvements and bug fixes for POPLOG Prolog V13:

      * The I/O channel 'user' has been fixed to always connect with the
        terminal (i.e. the standard input/output), even when loading a
        marked range from VED; this has improved the interaction between
        VED and SPY, BREAK etc.

      * The I/O predicates (CONSULT, SEE etc.) have been improved and
        made more robust. There is less danger of errors resulting from
        reading on closed devices; filename meta-characters are handled
        consistently; filenames given to CONSULT and RECONSULT can omit
        the '.pl' extension.

        * A bug in RECONSULT which meant that nested RECONSULTS acted like
        CONSULTS has been fixed; this means, for example, that programs
        which load the same library (directly or indirectly) more than
        once will now get just a single definition of the predicates in
        the library file.

      * The directives ?- and :- can now be used from Prolog top-level
        and a new HELP file, PLOGHELP * DIRECTIVES, has been introduced
        to describe their use.

      * The POP11 macros ?- and :- which read and evaluate single Prolog
        goals have been improved: there is no longer a danger of losing
        characters, and the switch to and from Prolog itemisation is
        handled correctly. These macros are now documented in

      * The POP11 procedure -prolog_readterm-, which reads a Prolog
        term, now uses Prolog (rather than POP11) itemisation.

      * A bug in the ASSERT and RETRACT mechanism has been fixed.

      * A bug which prevented non-integer numbers from unifying
        correctly in head matches has been fixed.

1986 -------------------------------------------------------------------

Oct 31 (Kathryn Seifert and A.Sloman)

    --- Major changes to the Prolog Help file system.  A new format has
    been introduced,  some files have been renamed, and some files have
    been removed.  PLOGHELP * HELP_CHANGES summarises changes.

    See PLOGHELP * HELPFILES and PLOGHELP * PROLOG for an overview of
    the structure of the new Prolog Help file system.

    --- VED-based access to Prolog library and documentation files when
    Prolog not loaded has been simplified by provision of:

    These can now be used for cross-references in files, invoked by

Oct 27 (John Gibson_
    --- Bug in library(modules) fixed.

May 11 (John Gibson)
    --- Two further Prolog bugs fixed. The first was introduced in the
    earliest Version 12 (unfortunately), and under certain conditions
    could cause the system to crash while creating a new Prolog variable.
        The second was much older (3 years or more), and caused the garbage
    collector to crash when it happened to be called inside -suspend- (while
    suspending a Prolog process). In particular, this could happen when a
    Prolog program was being run in Ved 'immediate mode' and requesting input
    (thus necessitating the suspension of the program).

Apr 22 (John Gibson)
    --- A bug concerned with numbering of prolog variables (_1, _2, etc) has
    been fixed. This occasionally caused the system to crash inside a garbage
    collection while -spy- was being used.

April 20th (John Gibson)
    --- In Version 12, Prolog performance has been substantially increased, on
    average around 30-35%. Prolog compilation has also been speeded up to a
    certain extent -- it is hoped that more improvements will follow.

March/April (Sak Wathansin)
    --- Bug fixes for V12 release:
        a) functor changed to behave as in DEC-10 Prolog
        b) ?- available from any file (not just .pl files as before)
        c) missing trailing "." when compiling from a Ved buffer (with CTRL-D)
           now gives a sensible error message (used to mishap with "Stack
        d) Calling conjuction/disjunction of undefined goals now gives
           "Unknown predicate" error which can be trapped with LIBRARY
            * UNKOWN

1985 ----------------------------------------------------

August 21 (Mark Rubinstein)
    --- Prolog code can be compiled inside Prolog documentation files,
    thanks to changed format for vedhelplist et cetera.

July 22 (Jonathan Laventhol)
    -- New Representation of Prolog Terms
        In summary:
            Prolog complex terms (other than pairs) now have their datatype,
            Uninstantiated Prolog variables now are represented by variables
            whose contents point to themselves.
            Uninstantiated Prolog variables print their underscore number in
    -- More code is now in the main POPLOG system
        This includes basic term manipulators and other utilities.
    -- Closer DEC10 Functionality
        functor/3 behaves properly.
        X = undef works.

February 28 (Jonathan Laventhol)
    ProGram version 5. See ProGram help file *CHANGES for full details.

1984 ------------------------------------------------------
December 5 (Mark Rubinstein)
    Bugs in LIB TRACER now fixed.  Previously it couldn't handle disjunction
    and couldn't be swithched off properly.

August 8
    ProGram version 4. See ProGram help file *CHANGES for full details.

March 29 (Jonathan Laventhol)
        *** VERSION 9 ***
    Many enhancements and bug fixes have been made.
    Please see PLOGNEWS CHANGES for full details

*** version 8.2.1 Prolog ***
*** version 8.1 prolog ***

September 20 1983 --------------------------------------------------------

Minor Bug fixed:
    ?- '[]' = [].
    now succeeds, in accordance with PDP11 and DEC10 Prolog systems.

September 5 1983 ---------------------------------------------------------

Bugs fixed:

    ?- help
        as the first goal of a prolog session now works with no argument.

    ?- atom([]).
        now succeeds, in accordance with PDP-11 and DEC10 Prologs.

    ?- functor(A, [], 0).
    ?- functor([], A, 0).
        now work, giving A = []

    ?- rename(Old, New).
        now works when renaming files

    ?- X = foo(1,2), X.
        now works

    ?- library/1 fixed to fail on backtrack

Documentation altered to specify:
    that cuts don't work in top level
    that conditionals don't work in top level

Library Additions:
    "log" added to library
    "module" added to the autoloadable directory.
    "undefs" added to autoloadable library.

*** version 8 prolog ***

    Many new features.  Please see PLOGHELP Changes.
    The help system has been altered so that from within Prolog you get a
    different set of help files.  Use PLOGHELP from POP11 for the same files.
    The file structures is now like this:
        [pop.plog.src]      the source files
        []     the help files
        [pop.plog.lib]      the library files
        []     autoloadable library files

28 June 1983 -------------------------------------------------------------
    abolish/2 is now in the library file USEFUL.PL, and will be in
    the new system.

13 June 1983 -------------------------------------------------------------
    library(findall) added.  from programming in prolog, page 152.

10 june 1983 -------------------------------------------------------------
    PLOGHELP and ENTER PLOGHELP added as temporary fix.
    HELP PROLOGBUILT split into separate files, accessable via PLOGHELP.

--- C.all/help/plognews.v14
--- Copyright University of Sussex 1993. All rights reserved.