Ann: SWI-Prolog 9.3.21

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Dear SWI-Prolog user,

SWI-Prolog 9.3.21 is ready for download. There are a large number of
changes, mostly involving the WASM (Web Assembly) version.

Debugger

The internals of the debugger have been changed considerably, allowing
the VM to yield (return with the ability to resume) on trace events.
Yield based and hook based (using prolog_trace_interception/4) reuse
the same code to communicate how execution must be continued after
prompting the user. The set of supported trace continuations has been
extended to simplify writing your own debugger.

The debugger rules to decide with ports to hide (or show) was modified
a little, notably tracing calls to built-in predicates called through
catch/3, findall/3, etc. Exception ports are now always visible,
trapping the debugger immediately on most exceptions. This notably
makes trap/1 more effective. trap/1 has been updated to avoid
trapping system calls immediately wrapped in catch/3. This implies
that calls like this do not trap the debugger.

catch(number_codes(Num, Codes), error(_,_), fail).

WASM version

Much improved support for dealing with SWI-Prolog engines. Support
for yield based debugging (required to run SWI-Tinker)

SWI-Tinker

Based on this, SWI-Tinker (the former SWI-Prolog WASM shell) now has
a (simple) debugger. Its internals are completely rewritten. The
JavaScript module tinker.js no exports five classes that provide
building blocks for building web pages that provide embedded of
interactive Prolog queries. SWI-Tinker can now exploit engines to
manage multiple open queries. This is definitely not perfect yet.
Help is welcome.

Misc

A few minor bug fixes.

  • wrap_predicate/4, used by tabling and trace/2 (possible double free).
  • SICStus block/1 emulation calling undefined predicate
  • resource/3 embedding calling undefined predicate.
  • PL_put_chars() added a reference to created atoms, preventing them
    from being garbage collected.
  • sparql_query/3 option endpoint(url) raised an exception
  • XPCE paste of Unicode text is fixed (X11 version)

Some regression, notably in the debugger, is not unlikely. Please report.

Enjoy --- Jan

SWI-Prolog Changelog since version 9.3.20

  • WASM: Fixed abort handling.

  • WASM: Fixed yieldable using Prolog.call() running in engine.

  • ENHANCED: trap/1: stop trapping direct catch. Do not trap the debugger
    for catch(SytemPred, _, _). Such calls are very unlikely interesting
    to the debugger.

  • ENHANCED: logic to trace a call to a system predicate Consider system
    with a stack user ← meta ← system as a debug frame. For example,
    trace char_code/2 in the code below.

    p1 :- catch(char_code(_,_), error(_,_), fail).

  • FIXED: finish command of GUI debugger. This fix adds skip(Frame)
    to the possible replies from prolog_trace_interception/4 and deletes
    prolog_skip_frame/1.

  • FIXED: prompt1/1 called in mode (-) must fail if there is no “first”
    prompt.

  • ADDED: Prolog.call(): allow passing the goal using Prolog.Compound()

  • FIXED: Prolog.Compound() constructor

  • ADDED: wasm_query/1, support running a single query interactively.

  • BUILD: Avoid CMake generating paths with double “/”

  • BUILD: Updated cmake_minimum_required to 3.10 as adviced in CMake 3.31

  • FIXED: Handling skip in the gui tracer. Incorrectly detected that
    an exit was from a skipped frame. We could also consider to move
    this into the exit port, e.g., present the port as exit(skip).

    The GUI tracer can be simplified as process_trace_action() is dealing
    with more details of handling the user continuation.

  • CLEANUP: Remove restoring REDO port from tracePort() This is dealt
    with in the VM backtracing code and (thus) never reached.

  • WASM: Fixed Prolog.consult() in strict mode

  • FIXED: #1352 open_resource/2: Unknown procedure: ‘$rc’:zip_close/2

  • ADDED: ansi_hyperlink/3: better handling of URLs

  • WASM: Rename shell to “tinker”. Tool will be named “SWI-Tinker”

  • WASM: More URL handling.

  • FIXED: PL_put_chars(): unregister atom when using PL_ATOM.

  • WASM: Support single character input from the user (get_code/1, etc.)

  • ADDED: prompt1/1 can retrieve current prompt using a variable.

  • BUILD: #1350 Auto-include utf8proc if documentation is requested.

  • WASM: Support include/1 from files loaded using a URL

  • FIXED: Sandbox: declare distinct/1,2 as safe (uses tries).

  • WASM: Allow reusing a query in the shell.

  • WASM: Added options to Prolog.consult() This allows for
    Prolog.consult(file1, file2, ..., {module:"project"})

  • WASM: Give proper warning on ?- [user].

  • WASM: Added decoding of ansi hyperlink sequence

  • WASM: Handle read/1 and friends in shell

  • MODIFIED: (Undocumented) PL_prompt_string() now returns UTF-8

  • WASM: Added tty_size/2 and get_single_char/1 to shell

  • WASM: Added upload and download buttons for WASM shell.

  • WASM: Simple debugger for the browser shell.

  • WASM: Added decoding of ANSI escape sequences

  • WASM: Prolog.call() provides nodebug option. Also add Prolog.Term()
    class that allows for creating terms from term handles or strings.

  • WASM: Split shell demo into multiple files.

  • WASM: Reorganised directory

  • WASM: Fixed dealing with heartbeat events.

  • DEBUG: Use swipl-web.js rather than swipl-bundle.js for debugging

  • WASM: Minimally working Prolog tracer in the browser

  • WASM: Fixed standard I/O flushing. Notably writing to user_error
    was flushed on a newline.

  • WASM: Fixed Prolog.write()

  • ENHANCED: Error message when using WASM await/2 in synchronous query.

  • FIXED: We must discard foreign environments While unwinding an
    exception, before we discard a frame, which may call the foreign
    cleanup handler, we must discard newer foreign environments.

  • FIXED: Extended query solutions from int to int64_t Otherwise,
    PL_new_solution() is limited to 2G solutions.

  • FIXED: PL_yield_address(): preserve foreign environment

  • FIXED: State handling using PL_yield_address().

  • FIXED: library(block) (SICStus emulation) warns about append/3.
    Reported by Peter Ludemann.

  • FIXED: wrap_predicate/4: possible double free after unwrapping The
    copy of the predicate held in the closure should not copy the lingering
    list and we must avoid lingering the wrapped supervisor as it becomes
    owned by the closure.

  • ADDED: Yield based debugger support This patch introduces a large
    number of changes to the VM as well as the debugger code. It allows
    interacting with the Prolog debugger using yield, i.e., instead of
    calling a hook when a Prolog port is passed it makes PL_next_solution()
    return. The environment can examine the state, make calls on this
    Prolog engine and finally set how the session must be continued and
    resume PL_next_solution().

    The interaction is similar to user:prolog_trace_interception/4, used
    to drive the GUI debugger using callbacks. Given this, it becomes
    possible to write a debugger for the WASM version for using in
    the browser. This can either be a traditional console debugger or
    a graphical debugger similar to the native debugger.

    This patch reorganises notably the backtracking and exception handling
    code in the VM, splitting these large pieces of code into many VM
    helper functions. It also reorganises several parts of the builtin
    debugger to facilitate code reuse between the callback and yield
    based debuggers.

    This is a squash commit of the trace-yield-state branch.

  • ADDED: print_prolog_backtrace/3: show_files(+How) option

  • CLEANUP: Delete VMI profiling code. As we have VMI functions and
    much better profiling tools this merely complicates the sources.

  • MODIFIED: abort/0: disable debug mode.

Package semweb

  • FIXED: sparql_query/3 using option endpoint(URL) This raised an
    exception in select_option/3 due to an insufficiently instantiated
    argument.

Package xpce

  • TRACER: Fixed “finish” to use new skip(Frame) reply.

  • FIXED: X11 version: paste Unicode text

1 Like
2

Thanks for continuos work on updating SWI-Prolog, Jan.

When activating swipl from Emacs Ediprolog, since some point of time I had to insert a line
open -a XQuartz like below. Otherwise spy command does not work
in Ediprolog mode. I have checked git source swipl whether new swipl version still requires that line with hope not being necessary now, but found it is not the case.

#! /bin/sh
SWIPL=${HOME}/bin/swipl
PACLIB=${HOME}/devel/zdd/prolog
PAC=${PACLIB}/pac.pl
ZDD=${PACLIB}/zdd/zdd.pl
open -a XQuartz
${SWIPL} -l $PAC -l $ZDD

Is there a way to omit the open -a XQuartz but spy command can be used ? I am afraid that the answer is NO knowing little about XQuartz.

3

I don’t know why spy/1 needs graphics unless it is redefined by ediprolog. Anyway, if it needs graphics it needs XQuartz on MacOS. I guess your open -a resolves that or you can add XQuartz to the autostart applications. On my machine it starts automatically while I have not touched the XQuartz configuration.

4

I have removed the line “open -a XQurtz”, and added XQuartz application to Login items so that it starts automatically. And spy works. Thanks.

However, if remember correctly, I did the same fix, but it did not work at that time.
And this time, as I happened to find that XQuratz was allowed as background in Privacy& Security setting. Also I remember that I changed XQuartz to a downloaded version from the one via Homebrew due to some reason which I don’t remember. Finally once I checked that the spy problem is not related to Ediprolog. Although I am curious of reason of the spy trouble, now it should be enough for me that auto-starting XQuartz seems to fix the trouble, Thanks again.

EDIT
I asked chatGPT ways of passing environmental variables (PATH for example) to Emacs (as GUI). It suggested four ways, only one of which I know. Although I am not sure whether they are related to the spy trouble, as three of them are new to me, I am curious on trying thems. BTW, it was surprise to see how widely and much chatGPT knows.