takes_less_than(4s), needs_less_than.
?- X = f(X). sto, X = f(X) % With occurs-check: fails or error | sto, loops. % Without occurs-check: may loopThis case is particularly ambiguous, as there is not a single system that loops here. Many systems loop when writing the answer, though. More explicitly:
?- X = f(X), Y = f(Y), X = Y. sto, false % occurs-check | sto, representation_error(term) % occurs-check error | sto, loops | sto, resource_error(...) % effectively implied by loops | sto, X = f(X), X = Y % rational trees | sto, X = f(f(Y)), Y = f(f(Y)) % literal substitution, Tau | sto, ... .
?- X = 1. 1 = X. % not an answer substitution
"✳54·43" ?- X is 1+1. X = 3, unexpected. % almost X = 1, unexpected. % too low X = 2.0, unexpected. % and after checking PM: X = 2.
... # Run a single quad file (two equivalent forms) make quad tests/predicates/assertz_quad.pl make quad QUAD_FILE=tests/predicates/assertz_quad.plThe first version does not work, the second does.
% Verify predicates exist ?- predicate_property(at_end_of_stream, built_in). true | predicate_property(at_end_of_stream, _).This is not an answer description!
?- X =:= foo. instantiation_error | type_error(evaluable,foo/0). ?- foo =:= X. idem.Because in 7.12:
When more than one error condition is satisfied, the error
that is reported by the Prolog processor is implementation
dependent.
% Negative argument fails ?- arg(-1, foo(a,b), X). false | error(domain_error(not_less_than_zero, -1), _).Should read just
?- arg(-1, foo(a,b), X). domain_error(not_less_than_zero, -1).
% Can't abolish static predicates % ?- abolish(append/3). % permission_error(modify, static_procedure, append/3).Why not:
?- abolish(abolish/1)). permission_error(modify, static_procedure, abolish/1) | permission_error(modify, static_procedure, ...).(It's not clear how you indicate modules, in case they appear ...)
% Abolish non-existent predicate (may succeed or error) ?- abolish(abolish_nonexistent_xyz/3). true | error(existence_error(procedure, abolish_nonexistent_xyz/3), _).This can never happen, however
| permission_error(modify, static_procedure, ...).might be possible. But since you implicitly imply qua the name that abolish_nonexistent_xyz/3 does not exist, it cannot happen. (But then note that we have again some implicit assumption, and testing should avoid such nonchalant implications.)
?- assertz(abolish_test(1)), assertz(abolish_test(2)), abolish(abolish_test/1), \+ current_predicate(abolish_test/1). true | \+ abolish_test(_).How can this alternative exist? The only alternative imaginable is
| permission_error(modify, static_procedure, ...).
?- asserta(X). error(instantiation_error, _).This insists on the second argument being a variable. Instead:
?- asserta(X). error(instantiation_error, ...). instantiation_error. % compact like in 13211-1 throw(error(instantiation_error, ...)).That is, all three are valid outcomes, and all three have to be tested. In answer descriptions variables represent variables (or some rational, infinite trees, but only when sto ...).
number_chars/2 extensively
after #28, #27, #19, #17,
% ugly hack because of unaddressed flowlog-prolog#19 glength([],0). glength([_|L],N1) :- glength(L,N2), N1 is N2+1. abs([]). abs([C|Cs]) :- ( C = a ; C = b ), abs(Cs). ?- length(L,16),(X=1;X=2),( abs(L), fail ; true ). L = [_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,_11,_12,_13,_14,_15], X = 1 ; % unexpected output ; L = [_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,_11,_12,_13,_14,_15], X = 2. ?- glength(L,N), N > 14, ( abs(L), fail ; true ). L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28], N = 15 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30], N = 16 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32], N = 17 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32,_34], N = 18 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32,_34,_36], N = 19 ; ... . ?- glength(L,N), N > 14, countall(abs(L),Cnt). L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28], N = 15, Cnt = 32768 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30], N = 16, Cnt = 65536 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32], N = 17, Cnt = 131072 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32,_34], N = 18, Cnt = 262144 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32,_34,_36], N = 19, Cnt = 524288 ; ... . ?- glength(L,N), N > 13, countall(abs(L),Cnt). L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26], N = 14, Cnt = 16384 ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28], N = 15, Cnt = 32768 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30], N = 16, Cnt = 65536 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32], N = 17, Cnt = 131072 ; % unexpected output ; L = [_0,_2,_4,_6,_8,_10,_12,_14,_16,_18,_20,_22,_24,_26,_28,_30,_32,_34], N = 18, Cnt = 262144 ; ... .
l(0). l(N0) :- l(N1), N0 is N1+1. ?- l(N). N = 0 ; N = 1 ; N = 2 ; N = 3 ; N = 4Segmentation fault (core dumped)
nihil --> [].This is a valid term, even if you do not have any DCG support. It should be at least a fact.
?- N is 2^63, functor(_,f,N). error(type_error(integer,9223372036854775808),functor/3), unexpected. type_error(...,...), unexpected. % any type error is bad ?- N is 2^63, arg(N,f(1),_). error(type_error(integer,9223372036854775808),arg/3), unexpected. false. % expected, but not found
outputs/1 with a grammar
rule body as argument. To start with, a list of characters will do.
?- call((write(3), call(1)).
outputs("3"),
type_error(callable, 1).
Compare this to the original example in 7.8.3.4:
call((write(3), call(1)). Outputs '3', then type_error(callable, 1).So it's outputs not output. The comma has here the meaning and then. Answer constraints and answer substitutions come last in a leaf-answer. (Unclear, if there are situations to put them first. Maybe if constraints and side effects are involved. But this gets way too complex.)
?- Ch = t, put_char(Ch).
outputs("t"),
Ch = t.
?- length(L,N). % #1 error(existence_error(procedure,length/2),length/2), unexpected. L = [], N = 0 ; ... . % expected, but not found ?- length(2,0). % #4 error(type_error(list,2),length/2), unexpected. false. % expected, but not found
?- current_op(Pri,Fix,'|'). Pri = 1150, Fix = xfy ; Pri = 1150, Fix = fy, unexpected.There must not be any such operator. Only the infix '|' is possible. See Cor.2#C2 and 8.14.3.4. Otherwise Flowlog is correct.
?- op(1150,fy,'|'). error(permission_error(create,operator,'|'),op/3). % nice ?- op(0,fy,'|'). true. % nice
?- append("ab","cd",L).
false, unexpected.
L = "abcd". % expected, but not found
?- append([],Ys,Zs).
Segmentation fault (core dumped)
Ys = Zs. % expected, but not found
?- append("a",Ys,Zs).
false, unexpected.
?- member(X,"a").
false, unexpected.
?- member(X,[a]).
X = a.
?- [X] = "a".
X = a.
cons([_|_]).
?- cons("a").
false, unexpected.
-0.0 as a number distinct
from 0.0. Therefore, they must be identical and print identically.
?- 0.0 == -0.0.
true. % good
?- writeq(-0.0).
outputs("-0.0"), unexpected.
outputs("0.0"). % expected, but not found
?- writeq(010). 10 true. % nice ?- number_chars(N,"010"). N = 8, unexpected. ?- number_chars(N,"08"). N = 8. % expected, but not found syntax_error(...), unexpected.
Flowlog (v4.6.14) Type 'help.' for help, 'halt.' to exit. ?- select(X,[1,2,3,4,5,6,7,8],_). X = 1 X = 3, unexpected % too early X = 6, unexpected X = 2 X = 7, unexpected ... ?- select(X,[1,2,3,4,5,6,7,8],_). X = 2, unexpected ... ?- select(X,[1,2,3,4,5,6,7,8],_),!. X = 2, unexpected. % sometimes, retry to see
inf :- inf. ?- inf. Segmentation fault (core dumped), unexpected. loops % expected | resource_error(...). % if you insist, ... but a WAM should loop
?- append([a], Ys, Zs).(above with default. Does work with interp. With wam:)Segmentation fault (core dumped), unexpected. Zs = [a|Ys]. % expected, but not found Ys = _1, Zs = [a|_2], unexpected.
?- append([a], Ys, Zs). Ys = Xs, Zs = [a|Xs], unexpected. % no longer Ys = _1, Zs = [a|_2], unexpected. % new
Xs come from?double_quoteschars as default. Like all new systems like
Scryer, 1ban, Trealla, Tau. And now also Flowlog!
ulrich@p0:/tmp$ git clone https://git.liminal.cafe/byakuren/flowlog.git Cloning into 'flowlog'... fatal: unable to access 'https://git.liminal.cafe/byakuren/flowlog.git/': gnutls_handshake() failed: Handshake failed ulrich@p0:/tmp$ cat /etc/issue Ubuntu 14.04.6 LTS \n \lThis does not happen with github. There I follow various systems like Scryer, Trealla.
?- select(X, Xs, Ys). false, unexpected. ?- select(X, Xs, Xs). false, unexpected. % see p.p.5.4 ?- select(X,Xs,[1,2,3]). false, unexpected. % this is the expected answer: Xs = [X,1,2,3] ; Xs = [1,X,2,3] ; Xs = [1,2,X,3] ; Xs = [1,2,3,X]. ?- select(X, [Y|nonlist], Xs). error(type_error(list,[_G0|nonlist]),/(select1,3)), unexpected.This type error would make sense, if the template and modes subclause would indicate
?list for the second argument, but it
reads
in p.p.5.2
select(?term, ?term, ?term)
?- Xs = [a|Xs], ( true ; catch(select(X, Xs, Ys), Err, true ) ). Xs = [a,a,a,a,a|...] ; Xs = [a,a,a,a,a|...], error(representation_error(term),/(select1,3)), unexpected. % expected behaviour: sto, false % occurs-check | sto, Xs = [a|Xs] % rational trees ; Xs = [a|Xs], X = a, Ys = [a|Ys] ; Xs = [a|Xs], X = a, Ys = [a|Ys] ; ..., ad_infinitum | sto, representation_error(term).A representation error can only be issued at a point in time when a goal attempts to create some term that cannot be represented. So this error prevents the creation of something. Thus the goal
Xs =
[a|Xs] may issue a representation error, if unification is
defined in such a manner (e.g., set_prolog_flag(occurs_check,
error) in Scryer or Trealla). But from above answer it is clear
that this goal succeeds, and thus the infinite tree is created. (Do
not call it an infinite term since terms are defined such
that there are no cyclic structures in them).
?- 62 = E, X is 2^E-1+2^E.
X = 9223372036854775807 % good
?- 62 = E, X is 2^E-1+2^E+1.
X = -9223372036854775808, unexpected.
?- X is 2^63.
error(evaluation_error(undefined),/(is,2)), unexpected.
evaluation_error(int_overflow) % expected exceptional value (3.66, 7.9.2 e, 7.12.2 g, 9.1.2)
| X = 9223372036854775808. % current_prolog_flag(bounded,false)
current_prolog_flag(bounded,false) in SICStus, Scryer,
Trealla, YAP, B, IF, IV, SWI, ECLiPSe, Ciao. Internally, these
implementations have two versions of integers, the small immediate
ones and the large one which reside on the heap. In this manner the
immediate integers may use less than 60..63 bits, which frees tagging
space for other uses.
Only GNU, 1ban with current_prolog_flag(bounded,true) and
correct overflows.
GNU:
| ?- 59 = E, X is 2^E-1+2^E. X = 1152921504606846975 yes | ?- 59 = E, X is 2^E-1+2^E+1. uncaught exception: error(evaluation_error(int_overflow),(is)/2)1ban:
?- 62 = E, X is 2^E-1+2^E. X = 9223372036854775807. ?- 62 = E, X is 2^E-1+2^E+1. 2026/01/02 11:43:26 error(evaluation_error(int_overflow),is/2)XSB, Cx, Minerva are also bounded, but miss some overflows.
In general, it is much easier to be conforming with unbounded integers, because this overflow evaluation_error never occurs which limits arithmetical optimizations. And one has to test for overflows anyway.
read-ing, consider writeq-ing. Such that
you always write valid syntax. So the first to address would be:
ulrich@gupu:/opt/gupu/flowlog$ ./flowlog Flowlog (pthreads) Type 'help.' for help, 'halt.' to exit. ?- number_chars(1,[_,[]]).error(instantiation_error,/(number_chars,2)), unexpected. type_error(character,[]). % expected,but notfound ?- number_chars(N,['3',.]). N = 3.0, unexpected. syntax_error(...). % expected, but not found ?- number_chars(N,[-,' ','1']). flowlog: fatal error (240): flowlog: unexpected token while parsing term
ulrich@gupu:/opt/gupu/flowlog$ ./flowlog Flowlog (pthreads) Type 'help.' for help, 'halt.' to exit. ?- read(X),catch(X,Err,true),writeq(X+Err),nl,fail. number_chars(N,[X]). number_chars(_1,[_2])+error(instantiation_error,number_chars/2) % good false ?- repeat,read(X),catch(X,Err,true),(X==end_of_file,!;writeq(X+Err),nl,fail). number_chars(N,[X]). % unexpected. Only C-d causes a reaction, newlines alone do not work here number_chars(_1,[_2])+error(instantiation_error,number_chars/2) X = end_of_file, Err = error(existence_error(procedure,/(end_of_file,0)),/(end_of_file,0))Also entering SPACE C-d instead does not work. This should flush the line and since it ends with ". ", the end-token is present already.
So how is it possible to write my own top level for the purpose of testing?
ulrich@gupu:/opt/gupu/flowlog$ ./flowlog
Flowlog (pthreads)
Type 'help.' for help, 'halt.' to exit.
?- set_prolog_flag(double_quotes,chars).
true
?- read(X).
"abc".
X = [a,b,c] % good
?- writeq("abc").
[97,98,99]true % unexpected
ulrich@p0:/opt/gupu/flowlog$ make cc -O2 -Wall -Wextra -pthread flowlog.c -lm -o flowlog flowlog.c:41:23: fatal error: stdatomic.h: No such file or directory #include^ compilation terminated. make: *** [flowlog] Error 1 ulrich@p0:/opt/gupu/flowlog$ cc --version cc (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4 Copyright (C) 2013 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
wget https://web.liminal.cafe/~byakuren/flowlog/flowlog.tar.gzgit clone https://git.liminal.cafe/byakuren/flowlog.git make