Quintus Prolog

`write_canonical/[1,2]`

Synopsis

write_canonical(+Term)

write_canonical(+Stream, +Term)

Writes Term to the current or specified output stream in standard syntax.

Arguments

Stream stream_object: a valid Prolog stream, which is open for output
Term term: the term to be written

Description

Equivalent to write_term/[2,3] with the options:

     [quoted(true),ignore_ops(true),numbervars(false),char_escapes(false)]

This predicate is provided so that Term, if written to a file, can be read back by read/[1,2] regardless of special characters in Term or prevailing operator declarations.

Does not terminate its output with a full-stop, which is required by read/[1,2].

In general, one can only read (using read/[1,2]) a term written by write_canonical/1 if the value of the character_escapes flag is the same when the term is read as when it was written.

Exceptions

Stream errors (see ref-iou-sfh-est).

Examples

The following sequence will succeed:

     ...
     open(FileName, write, StreamOut),
     write_canonical(StreamOut, Term),
     write(StreamOut, '.'),
     nl(StreamOut),
     close(StreamOut),
     ...
     open(FileName, read, StreamIn),
     read(StreamIn, Term),
     close(StreamIn),
     ...

To contrast write/[1,2] and write_canonical/[1,2]:

     | ?- write({'A' + '$VAR'(0) + [a]}).
     
     {A+A+[a]}
     
     | ?- write_canonical({'A' + '$VAR'(0) + [a]}).
     
     {}(+(+('A','$VAR'(0)),.(a,[])))

write_canonical/[1,2]