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listprologprolog-toplevel

How to expand a resulting list in SWI-Prolog?

?- length(L,25).
L = [_G245, _G248, _G251, _G254, _G257, _G260, _G263, _G266, _G
269|...].

If I use write(L) following the length predicate then the interpreter prints the list twice, one expanded and the other not.

Solution

  • There is a limit on the depth to prevent too long output. You can change it with set_prolog_flag/1.

    ?- length(L, 25).
L = [_G257, _G260, _G263, _G266, _G269, _G272, _G275, _G278, _G281|...].

?- current_prolog_flag(toplevel_print_options, V).
V = [quoted(true), portray(true), max_depth(10), priority(699)].

?- set_prolog_flag(toplevel_print_options, [quoted(true), portray(true), max_depth(100), priority(699)]).
true.

?- length(L, 25).
L = [_G257, _G260, _G263, _G266, _G269, _G272, _G275, _G278, _G281, _G284, _G287, _G290, _G293, _G296, _G299, _G302, _G305, _G308, _G311, _G314, _G317, _G320, _G323, _G326, _G329].

    Edit: You can also remove the limit completely by removing it from the options list.