- Prolog-standard - IMDEA Software

current_input/1, stream_property/2, set_input/1 on a closed stream handle
by Jose F. Morales 14 Jun '26

14 Jun '26

Dear all, I ran into something I don't quite understand about the treatment of closed streams. Take a closed stream handle: open(f, write, W), close(W), open(f, read, S), close(S) then: set_input(S) stream_property(S, _) reports existence_error(stream,S) while the ISO standard expects that: current_input(S) reports domain_error(stream, S). On the implementation side, it feels natural to share stream checking code, which would lead to a more uniform existence_error(stream,S) error for the three predicates (like SWI Prolog does). Am I missing something? Thanks, -- Jose

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Status of Archive changed?
by Ulrich Neumerkel 11 Jun '26

11 Jun '26

The link to https://lists.software.imdea.org/hyperkitty/list/prolog-standard@software.i… now just shows the message: This mailing list is private. You must be subscribed to view the archives. this worked so far. Is this change intended?

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char_conversion/2
by Jose F. Morales 09 Jun '26

09 Jun '26

Dear all, According to O'Keefe [1,2], char_coversion/2 was a mistake. Ciao Prolog does not implement char_conversion/2 at all. Support in other traditional systems is mixed (implemented for a small range 0-255, limited, or just drafted). More recent systems like Scryer or Trealla (if I am not wrong) seem to expose no implementation at all. There seems to be little incentive to implement a feature narrowly conceived, scarcely used, and dangerous in effect. I would like to propose flagging char_conversion/2 as obsolescent (still conforming, but marked as removal in any future revision, with existing implementations explicitly free to retain it as an extension). The C language had a similar issue with trigraphs, which have been removed (C23), and Fortran maintains a formal obsolescent-features list; so there is ISO precedent for retiring features. Cheers, [1] https://www.cs.otago.ac.nz/staffpriv/ok/pllib.htm [2] https://www.complang.tuwien.ac.at/ulrich/iso-prolog/pllib-2015-02-11.htm -- Jose

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max_integer flag on unbounded system
by Jose F. Morales 03 Jun '26

03 Jun '26

Hi Ulrich, Quick one about current_prolog_flag/2 when a standard flag is conditionally absent. On a system with bigints, flags max_integer and min_integer are not present. So what should ?- current_prolog_flag(max_integer, X). do there: fail, or raise domain_error(prolog_flag, max_integer)? At least Scryer (I've not checked other compliant systems) fails. Thanks, -- Jose

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max_arity vs max_procedure_arity
by Jose F. Morales 03 Jun '26

03 Jun '26

Dear all, representation_error(max_arity) is defined relative to the max_arity flag. That's fine for predicates like functor/3 and (=..)/2, but it's also specified for predicate-indicator predicates like abolish/1 and current_predicate/1. The trouble is that some systems make compound-term arity unbounded (or quite large) while still limiting predicate arity. On SWI: ?- functor(H, foo, 2000). % ok ?- functor(H, foo, 2000), assertz(H). % representation_error(max_procedure_arity) SWI Prolog solves the issues by splitting max_arity from max_procedure_arity (the latter isn't ISO). Eclipse Prolog also has two different limits but error is underreported (ambiguous). Picat, although not a Prolog system, also has two different limits (probably rooted in B-Prolog). That is definitely a problem and most of the ISO tests suites I have available either fail here or ignore those cases. Some possible directions: a) force one limit for terms and predicates (simplest but not a solution) b) raise limit for predicate arity (but that can be a *significant* implementation effort with low ROI) c) use max_procedure_arity (and push for future standardization) d) keep reporting max_arity for both limits, use error context (not standard) to disambiguate which arity limit has been reached I lean towards (c) looking for a possible change in the standard, or (d) as a temporary solution. (b) is difficult because some limits are intrinsically hard to raise in some engines (every reasonable computer language has some kind of procedure argument limits). A fallback calling convention may help but the implementation cost is not trivial. What are your opinions? Thanks, -- Jose

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WG17 meeting 2026, agenda
by Ulrich Neumerkel 13 May '26

13 May '26

Dear standardizer! This year's meeting will be held via Zoom, Monday, June 1st at 16:00 UTC (18:00 CEST) - 18:00 UTC JTC1 directives now permit experts that are not formal members of a national member body for two such meetings. Those experts need to be invited by me. In turn, the national member bodies will be informed about these invitations which in the long term may cause here some reaction by the national member bodies. Agenda 39th WG17 meeting 2026-06-01 16:00-18:00 UTC 1. Greeting and introduction of participants, administrativa 1.1 Minutes of 2025 meeting N306 1.2 Law as Code https://bmds.bund.de/themen/staatsmodernisierung/law-as-code https://www.sprind.org/en/actions/strategic-projects/law-as-code https://www.sovereign.tech/programs/standards https://vatmiraal.be/ 1.3 Unicode characters (TS 13211-4) https://www.metalevel.at/iso-prolog/unicode/ N307 1.4 Retaining clause numbering in existing standards. 2.1 Recent progress in Prolog systems New system Flowlog. https://web.liminal.cafe/~byakuren/flowlog/ https://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing#337 up to 364 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/number_chars_cont 2.2 Further corrigenda https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#62 up to 69 2.3 Syntax extension double bar https://www.complang.tuwien.ac.at/ulrich/iso-prolog/double_bar Currently supported by Ciao, Trealla, Modified Scryer. 2.4 Syntax extension digit separators https://www.complang.tuwien.ac.at/ulrich/iso-prolog/digit_separators Currently SWI, Trealla, Scryer partially, Modified Scryer. 2.5 Prolog prologue permutation/2 2.6 crypto_data_hash/3 https://www.metalevel.at/iso-prolog/crypto_data_hash https://github.com/mthom/scryer-prolog/issues/1137#issuecomment-4430540510 3. Other activities 3.1 Scryer meetups Duesseldorf 2025-11-13..14. Forthcoming, TU Wien, Vienna Saturday 2026-10-24, Sunday 2026-10-24. https://www.digitalaustria.gv.at/wissenswertes/events/scryerprologmeetup202…

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WG17 meeting 2025, agenda
by Ulrich Neumerkel 02 May '25

02 May '25

Dear standardizer! This year's meeting will be held via Zoom, Monday, June 2nd at 16:00 UTC (18:00 CEST) - 18:00 UTC JTC1 directives now permit experts that are not formal members of a national member body for two such meetings. Those experts need to be invited by me. In turn, the national member bodies will be informed about these invitations which in the long term may cause here some reaction by the national member bodies. Agenda 38th WG17 meeting 2025-06-02 16:00-18:00 UTC 1. Greeting and introduction of participants, administrativa 1.1 Minutes of 2024 meeting N301 1.2 Unicode characters (TS 13211-4) in stage 20.00 (NWIP approved, under development) https://www.metalevel.at/iso-prolog/unicode/ 1.3 DCG (TS 13211-3) in stage 60.00 (approved, under publication) Test cases https://www.complang.tuwien.ac.at/ulrich/iso-prolog/phrase 1.4 Retaining clause numbering in existing standards. 1.5 30 years of 13211-1 Resolved syntax ambiguity, NSTO, errors, char/code Japan, call/N, extension mechanism, constraints 2.1 Recent progress in Prolog systems https://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing#327 up to 336 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/number_chars_cont 2.2 Syntax extension double bar https://www.complang.tuwien.ac.at/ulrich/iso-prolog/double_bar 2.3 Comparison of handling (:-)/1 and (:-)/2 (action item 2024) https://www.complang.tuwien.ac.at/ulrich/iso-prolog/:- 2.4 DCG extension phrase//2 and phrase//3 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/phrase__N 2.5 Syntax extension digit separators https://www.complang.tuwien.ac.at/ulrich/iso-prolog/digit_separators 2.6 Prolog prologue 2.7 crypto_data_hash/3 https://www.metalevel.at/iso-prolog/crypto_data_hash 2.8 dif/2 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dif 2.9 Attributed variables 2.10 Further corrigenda https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#60 and #61 3. Other activities 3.1 Scryer meetups, Vienna 2024-11-07..08. Forthcoming, Duesseldorf Thursday 2025-11-13, Friday 2025-11-14.

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DTS 13211-3 ballot
by Ulrich Neumerkel 07 Apr '25

07 Apr '25

Dear standardizer! As a reminder, DTS 13211-3 is in ballot until April, 28th. For conformity of the related phrase/2, please refer to https://www.complang.tuwien.ac.at/ulrich/iso-prolog/phrase

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WG17 meeting 2024, agenda v2
by Ulrich Neumerkel 07 May '24

07 May '24

Dear standardizer! This year's meeting will be held via Zoom, Monday, June 3rd at 16:00 UTC (18:00 CEST). JTC1 directives now permit experts that are not formal members of a national member body for two such meetings. Those experts need to be invited by me. In turn, the national member bodies will be informed about these invitations which in the long term may cause here some reaction by the national member bodies. Agenda WG17 meeting 2024 1. Greeting and introduction of participants, administrativa 1.1 Minutes of 2023 meeting N298 1.2 Recent progress in Prolog systems https://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing https://www.complang.tuwien.ac.at/ulrich/iso-prolog/length 2. Further corrigenda https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#58 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#59 3. Prolog prologue 3.1 Review of p.p.10 foldl/4..6 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/prologue#foldl 3.2 Proposed additions 3.2.1 countall/2 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/countall 3.2.2 crypto_data_hash/3 https://www.metalevel.at/iso-prolog/crypto_data_hash 4. DCG progress https://www.complang.tuwien.ac.at/ulrich/iso-prolog/phrase 5. dif/2 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dif 6. Attributed variables 7. NWIP TS 13211-4 Part 4: Unicode characters in quoted Prolog text Ballot currently underway ---

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WG17 meeting 2024, agenda
by Ulrich Neumerkel 07 May '24

07 May '24

Dear standardizer! This year's meeting will be held via Zoom, Monday, June 3rd at 16:00 UTC (18:00 CEST). JTC1 directives now permit experts that are not formal members of a national member body for two such meetings. Those experts need to be invited by me. In turn, the national member bodies will be informed about these invitations which in the long term may cause here some reaction by the national member bodies. Agenda WG17 meeting 2024 1. Greeting and introduction of participants, administrativa 1.1 Minutes of 2023 meeting N298 1.2 Recent progress in Prolog systems https://www.complang.tuwien.ac.at/ulrich/iso-prolog/conformity_testing https://www.complang.tuwien.ac.at/ulrich/iso-prolog/length 2. Further corrigenda https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#58 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/stc#59 3. Prolog prologue 3.1 Review of p.p.10 foldl/4..6 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/prologue#foldl 3.2 Proposed additions 3.2.1 countall/2 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/countall 3.2.2 crypto_data_hash/3 https://www.metalevel.at/iso-prolog/crypto_data_hash 4. DCG progress https://www.complang.tuwien.ac.at/ulrich/iso-prolog/phrase 5. dif/2 https://www.complang.tuwien.ac.at/ulrich/iso-prolog/dif 6. Attributed variables ---

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