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


Predicates which read terms from the current input.


    ?- read(Term).
    ?- vread(Term, Env).


Both of these predicates unify Term with a term read from the current
input stream. Input is interpreted using the Dec10 Prolog 'LC'
convention (words starting with upper case letters denote variables) and
must be terminated with ".". Term is unified with the atom 'end_of_file'
if the input stream is at end of file.

Example:

    ?- read(Term).
    |: p(q(X), Y).
    Term = p(q(_1), _2) ?
    yes

'vread/2' also unifies Env with an environment associating variables in
Term with the names under which they occurred in the input. The
environment is a list of entries of the form:

    Name = Var

Example:

    ?- vread(Term, Env).
    |: p(q(X), Y).
    Term = p(q(_1), _2)
    Env = [Y = _2, X = _1] ?

    yes

The prompt used by 'read' and 'vread' can be changed with the predicate
'prompt/2' (see PLOGHELP * PROMPT).

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


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

PLOGHELP * I_O
 Overview of input/output operations in Prolog


--- C.all/plog/help/read
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