block declarations seem to be broken in recent release, sometime before v9.2.8

Using SWI-Prolog 9.2.8 on MacOS.

Attempt to declare a predicate as blockable, using the block/1 directive seems to put the runtime system in a broken state, so that it will no longer run predicates that have a block rule, nor predicates delayed using when/2.

If the block directive is removed, when/2 calls function normally.

This seems to apply to both sicstus and sicstus4 dialects. As far as I know, it worked fine before the sicstus4 update, but I'm not sure when that was.

Example:

When run on a fresh run of SWI, the following file content:

:- use_module(library(dialect/sicstus)).
:- use_module(library(clpfd )).

:- block mytest( - ).

mytest(a).
mytest(b).

% END

*** produces the following output:

Welcome to SWI-Prolog (threaded, 64 bits, version 9.2.8) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details.

For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word).

% library(prolog_wrap) compiled into prolog_wrap 0.00 sec, 10 clauses % sicstus/(block) compiled into block_directive 0.00 sec, 41 clauses % library(occurs) compiled into occurs 0.00 sec, 24 clauses % library(error) compiled into error 0.00 sec, 100 clauses % library(arithmetic) compiled into arithmetic 0.00 sec, 130 clauses % library(quintus) compiled into quintus 0.00 sec, 55 clauses % library(dialect/sicstus) compiled into sicstus 0.01 sec, 66 clauses % library(yall) compiled into yall 0.00 sec, 71 clauses % library(apply_macros) compiled into apply_macros 0.00 sec, 70 clauses % library(assoc) compiled into assoc 0.00 sec, 103 clauses % library(pairs) compiled into pairs 0.00 sec, 21 clauses % library(clpfd) compiled into clpfd 0.08 sec, 1,283 clauses % /Users/geraintwiggins/Library/Mobile Documents/com~apple~CloudDocs/Temp/Temp.pl compiled 0.09 sec, 8 clauses ?- mytest(a). ERROR: Unknown procedure: prolog_wrap:'$block_helper$mytest'/1 ERROR: In: ERROR: [13] prolog_wrap:'$block_helper$mytest'(a) ERROR: [12] '$wrap$mytest'(a)1-st clause of '$wrap$mytest'/1 ERROR: [11] toplevel_call(user:user: ...) at /Applications/SWI-Prolog.app/Contents/swipl/boot/toplevel.pl:1317 ?- when( ground(X), mytest(X)). when(ground(X), mytest(X)).

?- when( ground(X), mytest(X)),X=a. ERROR: Unknown procedure: prolog_wrap:'$block_helper$mytest'/1 ERROR: In: ERROR: [20] prolog_wrap:'$block_helper$mytest'(a) ERROR: [19] '$wrap$mytest'(a)1-st clause of '$wrap$mytest'/1 ERROR: [18] when:trigger_ground(a,user:mytest(a)) at /Applications/SWI-Prolog.app/Contents/swipl/library/when.pl:139 ERROR: [17] when:attr_unify_hook(call(when: ...),a) at /Applications/SWI-Prolog.app/Contents/swipl/library/when.pl:202 ERROR: [16] uhook(when,call(when: ...),a) at /Applications/SWI-Prolog.app/Contents/swipl/boot/attvar.pl:86 ERROR: [15] call_all_attr_uhooks(att(when,call(...),[]),a) at /Applications/SWI-Prolog.app/Contents/swipl/boot/attvar.pl:63 ERROR: [14] '$wakeup'(wakeup(att(when,...,[]),a,[])) at /Applications/SWI-Prolog.app/Contents/swipl/boot/attvar.pl:58 ERROR: [13] a=a ERROR: [11] toplevel_call(user:user: ...) at /Applications/SWI-Prolog.app/Contents/swipl/boot/toplevel.pl:1317 ERROR: ERROR: Note: some frames are missing due to last-call optimization. ERROR: Re-run your program in debug mode (:- debug.) to get more detail. ^ Exception: (4) setup_call_cleanup('$toplevel':notrace(call_repl_loop_hook(begin, 0)), '$toplevel':'$query_loop'(0), '$toplevel':notrace(call_repl_loop_hook(end, 0))) ?

=======================

When the block directive is removed, the when command, above, works correctly:

Welcome to SWI-Prolog (threaded, 64 bits, version 9.2.8) SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software. Please run ?- license. for legal details.

For online help and background, visit https://www.swi-prolog.org For built-in help, use ?- help(Topic). or ?- apropos(Word).

% library(prolog_wrap) compiled into prolog_wrap 0.00 sec, 10 clauses % sicstus/(block) compiled into block_directive 0.00 sec, 41 clauses % library(occurs) compiled into occurs 0.00 sec, 24 clauses % library(error) compiled into error 0.00 sec, 100 clauses % library(arithmetic) compiled into arithmetic 0.00 sec, 130 clauses % library(quintus) compiled into quintus 0.00 sec, 55 clauses % library(dialect/sicstus) compiled into sicstus 0.01 sec, 66 clauses % library(yall) compiled into yall 0.00 sec, 71 clauses % library(apply_macros) compiled into apply_macros 0.00 sec, 70 clauses % library(assoc) compiled into assoc 0.00 sec, 103 clauses % library(pairs) compiled into pairs 0.00 sec, 21 clauses % library(clpfd) compiled into clpfd 0.08 sec, 1,283 clauses % /Users/geraintwiggins/Library/Mobile Documents/com~apple~CloudDocs/Temp/Temp.pl compiled 0.10 sec, 4 clauses ?- when( ground(X), mytest(X)),X=a. X = a.

====================

Of course, block directives can be simulated using when/2, so this doesn't stop us using advanced prolog, but the behaviour does not match the manual, so that's why I raise it here.

Hope this helps.

Geraint

SWI-Prolog / swipl-devel

block declarations seem to be broken in recent release, sometime before v9.2.8 #1331