
print(+Stream, ?Term)

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



Arguments
   Stream              Stream handle or alias (atom)
   Term                Prolog term.

Type
   Term I/O

Description
   Used to print the term Term on the output stream Stream according to the
   current operator declarations, i.e.  the same as write/2, 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/2 was
   called from, it is used by print/2 in the following way:

  * If Term is a variable, it is printed using write/2.

  * If Term is a nonvariable or an attributed variable, then portray(Stream,
    Term) is called.  If it succeeds, so does print/2.  Otherwise, if Term is
    atomic, it is written using write/2 and the predicate succeeds.  If
    Term is a compound term, its main functor is printed using write/2 and
    print/2 is called recursively on its arguments.

   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/2, but not the list tails.  Thus e.g.  a list [1,2,3] will be
   passed once to portray/2 as a whole and then the elements 1, 2, 3, but
   not [2,3], [3] and [].

   If portray/2 is not visible but portray/1 is, it is called instead of
   portray/2, with the 'output' stream temporarily redirected to Stream.
   Because of this side effect, defining portray/2 is preferrable.

   portray/1, 2 is used by the system when printing the answer bindings
   in the top-level loop, and by the debugger to print trace lines.

   print(S, Term) is equivalent to write_term(S, Term, [portrayed(true),
   numbervars(true)]).

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


Note
   The output of print/2 is not necessarily in a form acceptable to
   read/1,2 and there is no 'printq' predicate.




Modes and Determinism
   print(+, ?) is det

Modules
   This predicate is sensitive to its module context (tool predicate, see @/2).

Exceptions
     4 --- Stream is not instantiated.
     5 --- Stream is not an atom or a stream handle.
   192 --- Stream is not an output steam.
   193 --- Stream is not a stream specification.

Examples
   
Success:
    ?- [user].
     portray(S, a) :- write(S, b).

     p(a).
     user   compiled 148 bytes in 0.00 seconds

    yes.
    ?- write(write(a)), nl, print(output, print(a)).
    write(a)
    print(b)
    yes.
    ?- trace.

    yes.
    Debugger switched on - creep mode
    ?- p(a).
      (1) 0  CALL   p(a) (dbg)?- output: write        ('o' typed)
      (1) 0  CALL   p(a) (dbg)?- output: display
      (1) 0  CALL   p(a) (dbg)?- output: print/writeq
      (1) 0  CALL   p(b) (dbg)?- creep
      (1) 0  EXIT   p(b) (dbg)?- creep

    yes.

Error:
     print(S, a(b,c)).         (Error 4).
     print("str", a(b,c)).     (Error 5).
     print(input, X).          (Error 192).
     print(nostr, X + 2).      (Error 193).





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