
writeclause(+Stream, ?Clause)

   The clause Clause is pretty printed on the output stream Stream .



Arguments
   Stream              Integer (stream number) or Atom (reserved or user-defined                symbolic stream name).
   Clause              A Prolog term.

Type
   Term I/O

Description
   Used to pretty print the clause Clause on the output stream Stream
   according to the current operator declarations.


   When reading Prolog clauses from one file, and then writing to another,
   the latter part can be done using writeclause/2.  This is because the
   clauses are terminated by a period and a newline, which are not retained
   by prolog.  writeclause/2 replaces these, and flushes the output.


   writeclause/1,2 knows about the special meaning of ,/2, ;/2, ->/2, fg
   -->/2 and :-/2 and prints the clause with the appropriate indentation of
   subgoals and some (redundant) parantheses to show the clause structure.
   Everything else is written as with writeq/1,2, so output of writeclause/1,2
   is readable for read/1,2.



Modes and Determinism
   writeclause(+, ?) 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 an integer.
   192 --- Stream is not an output stream.
   193 --- Stream is an illegal stream specification.

Examples
   
Success:
      ?- writeclause(output, f(1,2,3)), writeclause(output, h(2,3)).
      f(1, 2, 3) .
      h(2, 3) .
      yes.

      ?- writeclause(output, X + 2).
      _56 + 2.
      yes.

      ?- writeclause(output, a(k):-write(k)).
      a(k) :-
              write(k) .
      yes.

      ?- writeclause(output, (a:-write(k),date(K))).
      a :-
              write(k),
              date(_68) .
      yes.

      ?- open(file1,update,s), writeclause(s, X + 2), close(s).
      X = _72
      yes.
      [eclipse]: sh('cat file1').
      _72 + 2.
      yes.

      ?- set_stream(a,output), writeclause(a, (:- dynamic f/1)).
      :- dynamic f / 1 .
      yes.

      ?- writeclause(output, (head:-a1,a2;a3,a4->a5;a6)).
      head :-
                (
                    a1,
                    a2
                ;
                    (
                        a3,
                        a4
                    ->
                        a5
                    ;
                        a6
                    )
                ).
      yes.

Error:
      writeclause(S, a(b,c)).         (Error 4).
      writeclause("string" a(b,c)).   (Error 5).


See Also
   writeq / 2, writeclause / 1
