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print(?Term)

The term Term is written on the output stream according to the current operator declarations, using the predicate portray/2 or portray/1 if it exists.
?Term
Prolog term.

Description

Used to print the term Term on the current output according to the current operator declarations, i.e. the same as write/1, however the user has the possibility to influence the way the term is printed. If the predicate portray/2 is visible in the module where print/1 was called from, it is used by print/1 in the following way:

* If Term is a variable, it is printed using write/1.

* If Term is a nonvariable or a metaterm, then portray(output, Term) is called. If it succeeds, so does print/1. Otherwise, if Term is atomic, it is written using write/1 and the predicate succeeds. If Term is a compound term, its main functor is printed using write/1 and print/1 is called recursively on its arguments.

If portray/2 is not visible but portray/1 is, it is called instead of portray/2.

Note that when this predicate is used to print a list, only the elements of the list, i.e. the heads, are passed to the recursive calls of print/1, but not the list tails.

portray/1, 2 is used by the system when printing out the answer binding in the top-level loop to the answer_output stream and in the debugger, when the output command is set to print, to the debug_output stream.

As usual, the output is buffered, so it may need to be flushed (e.g. explicitly using flush/1).

Note The output of print/1 is not necessarily in a form acceptable to read/1,2.

Fail Conditions

None.

Resatisfiable

No.

Examples

Success:
    [eclipse]: [user].
     portray(S, a) :- write(S, b).
     user   compiled 100 bytes in 0.02 seconds

    yes.
    [eclipse]: print([a, b, c, d]).
    [b, b, c, d]
    yes.
    [eclipse]: [user].
     portray(S, '$VAR'(X)) :- write(S, a_), write(S, X).
     user   compiled 180 bytes in 0.00 seconds

    yes.
    [eclipse]: quintus.
    loading the library /usr/local/ECLIPSE/lib/quintus.pl
    loading the library /usr/local/ECLIPSE/lib/cprolog.pl
    loading the library /usr/local/ECLIPSE/lib/cio.pl

    yes.
    [eclipse]: numbervars(f(A, B, A, C), 1, X),
            write(f(A, B, A, C)).
    f($VAR(1), $VAR(2), $VAR(1), $VAR(3))
    B = a_2        % print/2 is used in the top-level loop
    A = a_1
    C = a_3
    X = 4
    yes.

See Also

display / 1, display / 2, print / 2, write / 1, write / 2, writeq / 1, writeq / 2