SWI-Prolog supports compilation of individual or multiple Prolog
source files into ‘Quick Load Files’. A ‘Quick Load
File’ (.qlf file) stores the contents of the file in
a precompiled format.
These files load considerably faster than source files and are
normally more compact. They are machine-independent and may thus be
loaded on any implementation of SWI-Prolog. Note, however, that clauses
are stored as virtual machine instructions. Changes to the compiler will
generally make old compiled files unusable.
Quick Load Files are created using qcompile/1.
They are loaded using
consult/1
or one of the other file-loading predicates described in
section 4.3. If consult/1
is given an explicit .pl file, it will load the Prolog
source. When given a .qlf file, it will load the file. When
no extension is specified, it will load the
.qlf file when present and up-to-date, and the .pl
file otherwise.
A .qlf file is up-to-date if the source it was compiled
from has not changed since. Whether it changed is decided by the
content of the source, a hash of which is stored in the
.qlf file, and not by its modification time: a tree that
arrives by checkout, copy, unpack or install carries times of its own,
in either direction. A source that is newer but unchanged is thus still
loaded from its .qlf file. If the source did change, the
.qlf file is recompiled when it can be written and the
source is loaded without it otherwise. Set the source
flag to ignore .qlf files altogether.
- qcompile(:File)
- Takes a file specification as consult/1,
etc., and, in addition to the normal compilation, creates a Quick
Load File from File. The file extension of this file is
.qlf.
The basename of the Quick Load File is the same as the input file.
If the file contains ‘:- consult(+File)’, ‘:-
[+File]’ or ‘:- load_files(+File,
[qcompile(part), ...])’ statements, the referred files are
compiled into the same .qlf file. Other directives will be
stored in the
.qlf file and executed in the same fashion as when loading
the
.pl file.
For term_expansion/2,
the same rules as described in
section 2.11 apply.
Conditional execution or optimisation may test the predicate
compiling/0.
Source references (source_file/2)
in the Quick Load File refer to the Prolog source file from which the
compiled code originates.
- qcompile(:File,
+Options)
- As qcompile/1,
but processes additional options as defined by
load_files/2. Options
are passed to load_files/2.
In addition the following options are processed:
- include(+Include)
- What to include into the QLF file. Currently accepts only a single
value: the atom
user. When specified, files loaded
indirectly from File that to not come from the Prolog library
are included into the .qlf file. This may be used to
generate a single file from an application. The result is comparable to
a save state (see qsave_program/2)
with the following differences:
- Only your application code is included. The Prolog libraries and
boot files are not.
- Only Prolog code is included,
.qlf files cannot include
arbitrary resources.
- The file can be loaded into a running Prolog process, while a saved
state can only be loaded into a virgin Prolog virtual machine.
