Ann: SWI-Prolog 8.1.22

jan · February 15, 2020, 3:15pm

Dear SWI-Prolog user,

SWI-Prolog 8.1.22 is available for download. This release comes with
three major changes. The impact on compatibility should be minimal, but
some regression is not unlikely. Highlights:

COMPATIBILITY: The addition of rational numbers required several
constants in SWI-Prolog.h to be changed. Foreign code is source
code compatible, BUT NOT BINARY. C code expecting to cover all
data types should process rational numbers. Binary serialization
of terms (library(fastrw) and PL_record_external()) is NOT
compatible.

The policy is to maintain compatibility at this level, so the above
is a sad exception.
Rational numbers (P/Q) as first class citizens. Support is largely
compatible with ECLiPSe thanks to the involvement of Joachim Schimpf.
Implementation of X^Rational by Rick Workman, as well as many of the
tests. Highlights:
- Rational numbers satisfy atomic/1 and number/1
- Integer is a sub-type of rational. The canonical form of
  P/1 is simply P.
- The syntax is e.g. 1r3.
- The flag prefer_rationals make all arithmetic that have a precise
  result as a rational number return a rational number instead of a
  float.
- The flag rational_syntax can be used to add 1/3 as preferred syntax.
Further implementation of ECLiPSe proposed support for IEEE-754
floating point arithmetic, allowing arithmetic to produce float
infinitity, NaN (not a number) and +/- 0.0 as opposed to an
exception. Default is the ISO Prolog behavior.
Support for controlled autoloading, i.e., define specific predicates
to be autoloaded from specific files. This can also be considered a
lazy equivalent to use_module/1,2. See autoloaded/1,2 and the
Prolog flag autoload. Most of the library now uses autoload/2
rather than use_module/1 or relying on general autoloading from the
library.

This may have some impact on stability. Libraries can only be auto
loaded if they have no impact on the global system such as defining
hooks or setting flags.

Not all extension packages fully support the new auto loading and
thus disabling autoloading only works with the core system and some
packages. Notably the HTTP infrastructure does not yet run without
autoloading.

Finally, some bugs are fixed. Matt Lilley fixed some of the SAML support
for the changes to certificate handling in SSL. A possible memory
corruption in tabling. is fixed. There is a start handling restraints
with tabling: consider results that cannot be computed due to resource
limitations as undefined.

Enjoy --- Jan

SWI-Prolog Changelog since version 8.1.21

TEST: Split the core test dir to support concurrent testing better
ADDED: Proper exponentiation (** and ^) for X^rat. Implemented by
Rick Workman.
DOC: Make library(simplex) documentation depend on GMP.
BUILD: Fixed compilation without GMP
ENHANCED: simplify Rat is Expr if Rat is instantiated to a rational
number.
MODIFIED: is/2 to unify the first argument instead of using arithmetic
equality if the left argument is instantiated.
FIXED: retractall/1: if decompiling a clause head raises a stack
overflow the clause is not retracted and retractall/1 succeeded.
Now retractall raises a resource error exception. Note that it may
have completed part of its job.
ADDED: connect_ugraph/3. Also added docs or complement/2 and
reachable/3.
ENHANCED: Trapping recursive autoloading, debug/3 and print_message/2.
Not really ideal yet, but at least a plain system error is avoided
and some context is provided.
FIXED: tty control on not really terminals for Unix-like systems.
Breaks single stroke interaction in e.g., swipl-win. Jan Burse.
AUTOLOAD: Support HTML to text conversion (lynx subdir of library).
MODIFIED: Make use_foreign_library/1,2 available as built-in
directives.
ADDED: Handle require/1 in library(prolog_xref).
ENHANCED: Make require/1 cooperate properly with autoloading.
Non-built-in predicates that are requested using require/1 are
mapped to autoload/2 calls. As a result, require/1 cooperates with
all modes of the autoload flags and prevents local (re-)definition
of required predicates.
ENHANCED: library(ansi_term): keep working of library(time) is not
installed.
MODIFIED: Moved exists_source/1 to built-in to simplify writing
conditional code.
ADDED: Autoload flag values user and user_or_explicit.
FIXED: Avoid the toplevel from counting on module inheritance.
CLEANUP: Avoid excessive library dependencies in library(shlib).
CLEANUP: Enable autoloading for many of the libraries that are almost
always loading. Reducing the number of file s loaded at startup from
33 to 12.
DEVEL: Avoid library(pure_input) and library(lists) dependency in
startup file used to run from the build directory. Reduces startup
time and avoids unnecessary dependencies.
ADDED: autoload/1,2, providing a controlled way to perform autoloading
of both libraries and application files. Controlled by the flag
autoload, which provides an additional value explicit, disabling
uncontrolled autoloading while keeping controlled autoloading.
Some re-organization of the autoload code.
MODIFIED: Renamed autoload/0,1 from library(prolog_autoload) to
autoload_all/0,1 to avoid a conflict with the new autoload/1,2
directive. As this library is normally used through saved-state
creation the impact should be minimal.
CLEANUP: Removed isDefinedProcedureSource() hack. No longer needed
since Keri Harris supported reloading as a proper transaction.
ENHANCED: print_term/2: integrate parts with Pengines term//2 to
convert a term into HTML. Used to avoid unnecessary spacing around
operators.
BUILD: Renamed CMake target prolog_products to core as this is
a too common step in the development cycle.
FIXED: Properly initialise the rational tripwire in a new thread.
ADDED: nexttoward/2 function.
ADDED: ECLiPSe compatible IEEE 754 floating point arithmetic. This
commits provides four flags to make floating point arithmetic return
special values (Inf, NaN, -0.0) rather than raising an exception
and supports setting the float rounding mode. Not all arithmetic
has been updated to fully suppor these flags.
ADDED: Extend (tabling) tripwire system to deal with very large
rational numbers.
MODIFIED: rdiv/2 function to throw a type error if an argument is
a float.
DOC: rational numbers are always decimal.
ADDED: abolish_private_tables/0 and abolish_shared_tables/0.
TEST: Rational tests by Rick Workman.
FIXED: rational/3 (possible crash)
MODIFIED: Sync rational syntax with ECLiPSe, always accepting
1r3 and 1/3 if rational_syntax is set to natural.
FIXED: PL_term_type() return PL_RATIONAL. This renumbers the PL_*
types in SWI-Prolog.h! We accept this as a lot of the header has
changed anyway for supporting rational numbers. Rick Workman.
FIXED: MPQ handling for in skipArgs().
DOC: Updated docs for the (/)/2 (division) function.
DOC: PL_is_rational().
CONFIG: Add rational settings to customize/init.pl
FIXED: in_temporary_module/3: avoid possible races.
FIXED: Avoid race if two threads try to create a temporary module
with the same name.
ENHANCED: Reduce the risk that the random/1 function start at the same
value in multiple threads if we do not use the GMP random functions.
MODIFIED: Changed rational defaults to be conservative, i.e., set
prefer_rationals to false and rational_syntax to compatibility.
Documentation invites people to evaluate the defaults we would like to
see in the future, prefer_rationals = true and rational_syntax =
natural.
FIXED: Pushing rational arguments when using optimized arithmetic.
DOC: statistics/2, thread_cputime
FIXED: Q/P with MPZ numbers still yielded a float if prefer_rationals
is true.
ADDED: PL_get_float() to succeed on MPZ and MPQ numbers (already
did integers).
FIXED: is/2 on instantiated rational, e.g. 1/3 is 1/3.
FIXED: Saving rationals to QLF files (thus also saved states)
FIXED: Compilation of MPZ/MPQ integers in the head
ADDED: Support rationals in library(prolog_colour).
ADDED: Prolog flag rational_syntax with values natural,
compatibility and none
ADDED: rational_syntax flag as module-sensitive flag with values
natural, compatibility and none.
MODIFIED: Renamed rational flag to prefer_rationals.
PORT: Allow building the system without GMP.
FIXED: Make rational branch compile without gmp
DOC: Rational number support.
ADDED: list_rationals/0,1
DOC: The Prolog flag rational
ADDED: ECLiPSe compatible functions numerator/1 and denominator/1.
MODIFIED: ^ now does rational arithmetic.
TEST: Generalize tests to deal with rational numbers.
ADDED: Prolog flag rational.
MODIFIED: PL_get_nchars() and PL_get_wchars() to support rationals.
This changes the flag values for the these functions (CVT_* and BUF_*),
making binary extensions incompatible. Source code remains compatible.
MODIFIED: Added rational numbers as first class atomic citizens rather
than a term numerator/denominator. Reserve a bit to distinguish
mpz and mpq on the stack
FIXED: Use-after-free error when dealing with updated answers for
answer subsumptive tabling.
FIXED: Unification from trie nodes. Could leave the argument stack
in a modified state.
FIXED: Memory leak when unifying a trie term fails due to an exception.
FIXED: Possible crash in tabling after an exception during tabling.
ADDED: Declare not_exists/1 from tabling as safe.
ADDED: Tabling meta predicates to xref.
XSB: Pass on tabling restraint options in the compatibility library.
DOC: More work on the documentation for restraints.
FIXED: delays_residual_program/2 if conditions is not ground.
ADDED: Partial support for tabling restraints. Currrently deals with
max_answers(Count) and provides the tabling options and Prolog flags
to deal with radial restraints.
MODIFIED: format_types/2 now throws an exception if the format
is invalid.
ADDED: list_format_errors/0,1, by default called from check/0.
FIXED: list_redefined/0: suppress messages for table aux predicates.

Package archive

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.

Package clib

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.
ADDED: support autoload for library(time).

Package clpqr

ENHANCED: Minimal changes to support disabled autoloading. This
package requires some serious reconsiderations of the relations
between modules. As is, it refers to many undefined predicates that
are not actually called and performs a lot of cross-module calls.
FIXED: the bug in issue https://github.com/SWI-Prolog/issues/issues/93
and in issue https://github.com/SWI-Prolog/issues/issues/63

Package cql

PORT: Allow compiling without rational number support.
FIXED: Missing argument in format/2 call.

Package http

FIXED: append argument order in auth_expansion authentication did
not expand the request because the appnd in auth_expansion failed
(wrong argument order)
FIXED: library(http_open): Include the path/1 in the parsed URL
so that http_cookie can correctly use it to identify cookies with
specific paths to be included in requests. Failure to include path/1
means that http_cookie will default to / which is not correct
FIXED: Communicated HTTP status code if this was set using the CGI
Status: code command.
TEST: Make test robust against rationals.
FIXED: Excess argument in debug/3 call.

Package jpl

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.
COMPAT: Updated PL_* and CVT_* constants due to renumbering to
include rationals.

Package libedit

CLEANUP: Make libedit use the new autoloader to reduce its footprint,
notably if it is not used.

Package ltx2htm

ENHANCED: handle LaTeX ``word’’ and `word’.

Package paxos

FIXED: Fixed format template in debug/3 message

Package pengines

ADDED: Support rational numbers in term --> HTML conversion.
FIXED: term//2 from library(http/term_html) to use priority 999 for
list elements.

Package pldoc

FIXED: Help index generation for division functions (/ and //).
ADDED: Determinism mode undefined to deal with the well founded
semantics status.
FIXED: PlDoc rendering for source code: too many arguments for
format/3.

Package protobufs

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package

Package semweb

MODIFIED: Turtle parser: if input is a text stream assume that the
encoding is correct. This avoids a permission error if the stream
(for example) originates from open_stream/2.

Package sgml

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.
FIXED: library(c14n2): Preserve namespaces belonging to attributes
in the element when canonicalizing.

Package ssl

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.
FIXED: Update library(saml) to use new crypto API
FIXED: library(xmldsig) updated to use the new certificate API and
use the nominated canonicalization method
FIXED: library(saml) needs to be updated to use the new certificate
API - in particular, two certificates cannot be compared using
unification anymore

Package xpce

FIXED: Browsing in right panel of profiler.
AUTOLOAD: Get basics of PceEmacs and graphical debugger working with
disabled autoloading.
AUTOLOAD: Working on autoload-safe operation for xpce and PceEmacs.
FIXED: Graphical debugger: avoid duplicate option key expose
(crashes new print_term/2).
FIXED: force float arithmetic as xpce cannot handle rationals (yet).
ADDED: PceEmacs to support rationals

Package yaml

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.

Package zlib

AUTOLOAD: Add explicit autoload/2 statements to all libraries provided
by this package.

j4n_bur53 · February 16, 2020, 3:55pm

Concerning:

Are the new flags documented somewhere. I checked current_prolog_flag/2 documentation,
but they are not yet listed. But it seems that flags are already there, like for example:

SWI-Prolog (threaded, 64 bits, version 8.1.22)

?- current_prolog_flag(float_rounding, X).
X = nearest.

Interestingly concerning ECLiPSe Prolog, they seem to only exist on paper.
I get for example with -L iso command line:

ECLiPSe Version 7.0 #52 (x86_64_nt)

[eclipse 1]: current_prolog_flag(float_rounding, X).
No (0.00s cpu)

Using get_flag/2 in non-iso mode doesn’t help either.
So I even don’t know how to compare with ECLiPSe Prolog.

jan · February 16, 2020, 4:23pm

Yes, but the float_rounding flag escaped documentation. Docs are in the git version.

ECLiPSe has bounded reals (breal) that provides an elegant alternative to playing with the float rounding flag. I think ECLiPSe doesn’t implement mapping evaluation_error to NaN either (yet).
@ridgeworks needs these and following this proposal makes sense to me. Joachim Schimpf knows a lot more about floats than I do

SWISH now runs 8.1.22 with some additional patches wrt. comparison to NaN and two work-in-progress notebooks dealing with rationals and floats SWISH Prolog tutorials

ridgeworks · February 16, 2020, 4:49pm

Very good progress on the arithmetic side; certainly more than I expected a couple of weeks ago.

As noted this is still a work in progress. I’ve now got over 300 unit test cases (assertions) with a little over 50 failing. Nothing catastrophic; mainly sign issues on IEEE special values and probably much fewer root causes than failures. I’ll put a more detailed report on the IEEE 754 discussion over the next couple of days.

For those interested in trying the nan value for the float_undefined flag, be aware that it’s behavior may appear quite illogical. It’s a number which is not a number. So nan =\= nan is true; all the other arithmetic comparisons which have a nan argument are false. But nan == nan (identity) at the term level.

Also for all number(X), X =:= min(X,nan) and X =:= max(X,nan).

The purpose of a nan continuation value is to avoid testing the result of each subexpression in a larger expression; just check the final result. But it should probably be treated as an application level error at that point and discarded. It probably isn’t the answer you want.

jan · February 16, 2020, 5:02pm

I am a bit surprised. After all, the resulting X is tainted. Checking the ECLiPSe proposal we find this, so I think we should go for a X instead of NaN.

min(NaN,Any) Any see below
max(NaN,Any) Any see below

IEEE 754 (2008) specifies minNum() and maxNum() in this way, i.e. preferring the non-NaN argument. [KAH] says there are good reasons to do so, but that they are disputed.

ridgeworks · February 16, 2020, 9:27pm

Also from C11:

F.10.9.2 The fmax functions
1 If just one argument is a NaN, the fmax functions return the other argument (if both
arguments are NaNs, the functions return a NaN).


F.10.9.3 The fmin functions
1 The fmin functions are analogous to the fmax functions (see F.10.9.2).

I agree it does seem weird, but there’s nothing normal about NaN’s.

peter.ludemann · February 16, 2020, 10:47pm

I’m seeing some warnings/errors that I didn’t see before:

Warning: /usr/lib/swi-prolog/library/pprint.pl:284:
Warning:    Variable not introduced in all branches: Arg

ERROR: /usr/lib/swi-prolog/library/prolog_codewalk.pl:40:38: Syntax error: Operator expected
ERROR: /usr/lib/swi-prolog/library/prolog_codewalk.pl:40:38: Syntax error: Operator expected
% Disabled autoloading (loaded 75 files)

The “Disabled autoloading” seems to be because of one instance of :- set_prolog_flag(autoload, false). … it would be nice if this warning had some source information with it. The error message is also related.
I haven’t tracked down why prolog_codewalk is being loaded … is there a way to trace the "load_module"s and similar directives?

swi · February 17, 2020, 7:05am

Compiling gets stuck generating INDEX.pl:

[....regular cmake stuff here...]
Cleaning... 0 files.
PGO: Compiling instrumented version
[1706/1707] Generating ../home/library/INDEX.pl
<---- stuck here, even after 20 minutes --->

I am using the following to compile (from archlinux PKGBUILD bash script):

#...some vars and other PKGBUILD stuff before this...
 mkdir -p build
  cd build
  cmake ../swipl-$pkgver \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=/usr \
    -DCMAKE_C_FLAGS="$CFLAGS -fPIC -ffile-prefix-map=$PWD= -w" \
    -DLIBEDIT_LIBRARIES=/usr/lib/libedit.so.0 \
    -DLIBEDIT_INCLUDE_DIR=/usr/include \
    -G Ninja
  ../swipl-$pkgver/scripts/pgo-compile.sh
  ninja

Is there a problem with the pgo-compile.sh ?

EDIT: this was working fine for 8.1.21; the compilation above was done using a clean source tree.

EDIT2: Seems the problem happens only when the cmake build directory is at the same as the swipl-8.1.22 directory.

jan · February 17, 2020, 7:57am

This is indeed the case. The code was also wrong. In general though, this message is by default disabled as it produces far too many false positives. It has nothing to do with autoloading AFAIK.

This has to do with loading order and missing (). Pushed fixes for both.

See source_file_property/2, property load_context(Module, Location, Options).

jan · February 17, 2020, 8:00am

Thanks. The Macports build bot also complains about this issue. I haven’t seen it in any test nor for building the system on various servers or the Ubuntu PPA build. Macports insists in building in the source tree though (not making a build dir). Seems the level of the build directory is involved in this. No clue how this relates to the changes in this version, but if this reproduces it should be possible to find out.

peter.ludemann · February 17, 2020, 8:35am

AFAIK, the only change I made was upgrading from 8.1.21 to 8.1.22. So, the message might have nothing to do with autoloading, but it probably has something to do with 8.1.21->8.1.22.

As for the “% Disabled autoloading (loaded 75 files)” message – is it possible to add something to indicate what caused that message? Is it triggered by set_prolog_flag(autoload,false) or by something else?

jan · February 17, 2020, 8:50am

Sure. The library changed

This message is only triggered by disabling autoloading completely.

jan · February 17, 2020, 9:30am

Pushed a fix for that.

swi · February 17, 2020, 7:52pm

Thanks! I think you are still the most responsive maintainer in the open source world

huda · June 15, 2022, 4:31am

I’ve just upgraded from 7.6.4 and it appears I need to update a lot of my predicates that rely on unification of float terms

fraction(A rdiv B, A, B).

?- fraction(2r3, A, B). 
false.

Is there an easy replacement to unify with 2r3 ?

Sorry if the question doesn’t make sense. I am not fluent in either English or Prolog!

CapelliC · June 15, 2022, 5:53am

The notation 2r3 has been added recently, then your code should continue to work unchanged, I think…

?- X rdiv Y = 2r3.
false.

?- X rdiv Y = 2 rdiv 3.
X = 2,
Y = 3.

huda · June 15, 2022, 6:09am

It isn’t, unfortunately, as you’re kind of found in your first example. And I’m not sure how to unify with the new notation.

?- set_prolog_flag(prefer_rationals, true).
true.

?- A is 2/3.
A = 2r3.

?- A is 2/3, A = N rdiv D.
false.

?- rational(2r3).
true.

?- rational(2 rdiv 3).
false.

jan · June 15, 2022, 7:39am

As of V8, rational numbers are primary citizens and thus a rational is atomic, a number and a super-type of integers. There is rational/3 to break it into pieces, so

 ?- A is 2/3, A = N rdiv D.

becomes

 ?- A is 2/3, rational(A, N, D).

That does require updates to your code. With some luck some clever replacements may do the trick. Possibly goal_expansion/2 can also do the trick. As is, rational/3 does not work in mode rational(-,+,+). If adding that mode solves a real problem we can add that.

P.s. better upgrade to 8.4 or 8.5 in one go

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