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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2021, VU University Amsterdam
    7                              SWI-Prolog Solutions b.v.
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
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   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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   34*/
   35
   36:- module(fastrw,
   37          [ fast_read/1,                % -Term
   38            fast_write/1,               % +Term
   39            fast_read/2,                % +Stream, -Term
   40            fast_write/2,               % +Stream, +Term
   41            fast_write_to_string/3      % +Term, -String, ?Tail
   42          ]).   43:- autoload(library(lists),[append/3]).

Fast reading and writing of terms

This library provides the SICStus and Ciao library(fastrw) interface. The idea behind this library is to design a fast serialization for Prolog terms. Ideally, this should be portable between Prolog implementation. Unfortunately there is no portably binary term format defined.

The current implementation is based on PL_record_external(), which provides a binary representation of terms that is processed efficiently and can handle subterm sharing, cycles and attributed variables. In other words, this library can handle any Prolog term except blobs such as stream handles, database references, etc. We try to keep the format compatible between versions, but this is not guaranteed. Conversion is always possible by reading a database using the old version, dump it using write_canonical/1 and read it into the new version.

This library is built upon the following built in predicates:

Compatibility
- The format is not compatible to SICStus/Ciao (which are not compatible either). Future versions of this library might implement a different encoding.
bug
- The current implementation of fast_read/1 is not safe. It is guaranteed to safely read terms written using fast_write/1, but may crash on arbitrary input. The implementation does perform some basic sanity checks, including validation of the magic start byte. */
To be done
- Establish a portable binary format.



 fast_read(-Term)
The next term is read from current standard input and is unified
with Term. The syntax of the term must agree with fast_read /
fast_write format. If the end of the input has been reached,
Term is unified with the term end_of_file.


   87fast_read(Term) :-
   88    fast_read(current_input, Term).



 fast_write(+Term)
Output Term in a way that fast_read/1 and fast_read/2 will be
able to read it back.


   95fast_write(Term) :-
   96    fast_write(current_output, Term).



 fast_write_to_string(+Term, -String, ?Tail)
Perform a fast-write to the difference-slist String\Tail.


  102fast_write_to_string(T, S, R) :-
  103    fast_term_serialized(T, String),
  104    string_codes(String, Codes),
  105    append(Codes, R, S)