A.17 library(fastrw): Fast reading and writing of terms

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.

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:

• fast_term_serialized/2 translates between a term and its serialization as a byte string.
• fast_read/2 and fast_write/2 read/write binary serializations.

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.

fast_write(+Term)

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

fast_write_to_string(+Term, -String, ?Tail)

Perform a fast-write to the difference-slist String\Tail.