PLOGHELP WRITE                                Chris Mellish, August 1982
                                   Revised by Robert Duncan, August 1989


Predicates which write a term to the current output.


    ?- write(Term).
    ?- vwrite(Term, Env).


Both of these predicates write Term to the current output stream, taking
account of any current operator declarations. Uninstantiated variables
in Term are written as an underscore ("_") followed by a number: the
numbers are not significant except that in any single call of 'write' or
'vwrite', variables printed with the same number are guaranteed to be
sharing.

Example:

    ?- write('Solution: '), write(sqrt(X) + 1), nl.
    Solution: sqrt(_1) + 1
    X = _1 ?
    yes

The second argument to 'vwrite/2' is an environment such as that
returned by 'vread/2' (see PLOGHELP * READ) which associates variables
with atomic names: any uninstantiated variable which occurs in Term and
which has an entry in Env is written out as the corresponding atom.

Example:

    ?- write('Solution: '), vwrite(sqrt(X) + 1, ['X' = X]), nl.
    Solution: sqrt(X) + 1
    X = _1 ?
    yes

Note: 'write/2' is available as a a synonym for 'vwrite/2', for
compatibility with other Prolog systems.


-- RELATED DOCUMENTATION ----------------------------------------------

PLOGHELP * I_O
 Overview of input/output operations in Prolog

PLOGHELP * PRINT
 Predicate which prints argument to current output.

PLOGHELP * PORTRAY
 Predicate which changes the action of the 'print' predicate.

PLOGHELP * DISPLAY
 Predicate which writes argument to current output in prefix format

PLOGHELP * WRITEQ
 Special form of 'write' predicate. Puts atom quotes around atoms which
 need them.


--- C.all/plog/help/write
--- Copyright University of Sussex 1989. All rights reserved. ----------