[FIXED] How to send EOF on Prolog swipl REPL on Windows to close the pseudo user file?

Issue

I'm using the swipl.exe Prolog REPL on Windows and trying to use the user pseudo file opened with [user]. but I can't figure out the key shortcut to leave the pseudo file:

c:\code>swipl.exe
Welcome to SWI-Prolog (threaded, 64 bits, version 8.0.3)

1 ?- [user].
|: hello :- format('Hello world~n').
|: ^Z

.

ERROR: user://1:9:3: Syntax error: illegal_character
|:
Action (h for help) ? ^C
c:\code>

Starting at the ^Z I typed the keys

• CTRL+Z
• ENTER (I expected here should have sent the EOF)
• ENTER
• .
• ENTER (this shows an error, and puts me back into the pseudo file)
• CTRL+C (this kills only one of the two swipl processes, leaving the console in a broken state with some keystrokes going to swipl and some going to cmd(!))

---

I know that on a blank line pressing CTRL+Z then ENTER normally works to send EOF, like if in more.com I type A ENTER B ENTER CTRL+Z ENTER everything works on my terminal.

---

If I run the swipl-win.exe GUI following the same key steps, immediately when I press CTRL+Z it closes the pseudo file and returns me to the top-level query:

?- [user].
|: hello :- format('Hello world~n').
|: 
% user://1 compiled 0.00 sec, 1 clauses
true.

?- hello.
Hello world
true.

?- 

---

What do I press to get [user]. to work in swipl.exe?

Solution

As you noticed, when you type [user], you're consulting a pseudo source file, which is made of terms. Therefore, simply type the term end_of_file. For example:

?- [user].
|: a.
|: b.
|: end_of_file.

% user://1 compiled 0.00 sec, 2 clauses
true.

Answered By - Paulo Moura

Answer Checked By - Robin (PHPFixing Admin)

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[FIXED] How to print this in one line statement in Prolog

Issue

How can i print this string in prolog in the best way:

predicate([], L, Id, L2):-
   length(L2, N),
   write('The length '),
   write(Id),
   write(' is '),
   write(N),
   write(' elements.'),
   nl.

Solution

In SWI-Prolog, you can use the built-in predicate format/2:

predicate([], L, Id, L2):-
   length(L2, N),
   format('The length of ~w is ~w elements\n', [Id, N]).

Answered By - slago

Answer Checked By - Senaida (PHPFixing Volunteer)

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[FIXED] How to list the clauses inside a module in SWI-Prolog?

Issue

SWI-Prolog has for example the library(dcgbasics) for use with DCGs.

While referencing the module is easy with use_module/1, e.g.

:- use_module(library(dcg/basics)).

trying to use listing/1 with it is not so easy.

?- listing(dcg:_).
true.

?- listing(dcgbasics:_).
true.

?- basics:listing.
true.

What is the correct way to get a listing of the clauses in library(dcg/basics)?

---

Follow up after answer given.

To list a specific clause, e.g. blanks//0 the query is

?- listing(dcg_basics:blanks).
blanks(A, B) :-
    blank(A, C),
    !,
    D=C,
    blanks(D, B).
blanks(A, A).

true.

Solution

Use either:

?- dcg_basics:listing.

Or:

?- listing(dcg_basics:_).

The first argument of use_module/1-2 is a file specification, not a module name. But listing the module contents requires the actual module name, which may be different (as it is the case here) from the module file basename. But how to find the module name from the file specification? In the particular case of SWI-Prolog:

?- absolute_file_name(library(dcg/basics), Path, [extensions([pl])]),
   module_property(Module, file(Path)).
Path = '/Users/pmoura/lib/swipl/library/dcg/basics.pl',
Module = dcg_basics.

Answered By - Paulo Moura

Answer Checked By - Willingham (PHPFixing Volunteer)

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