This chapter describes the features of SWI-Prolog for delivering applications that can run without the development version of the system installed.
A SWI-Prolog runtime executable is a file consisting of two parts. The first part is the emulator, which is machine-dependent. The second part is the resource archive, which contains the compiled program in a machine-independent format, startup options and possibly user-defined resources; see resource/3 and open_resource/3.
These two parts can be connected in various ways. The most common way
for distributed runtime applications is to concatenate the two
parts. This can be achieved using external commands (Unix:
cat, Windows: copy), or using the
stand_alone option to qsave_program/2.
The second option is to attach a startup script in front of the resource
that starts the emulator with the proper options. This is the default
under Unix. Finally, an emulator can be told to use a specified resource
file using the -x command line switch.
stand_aloneoption, the resource is headed by the emulator, a Unix shell script or nothing. Options is a list of additional options:
runtime, only read resources from the state (default). If
kernel, lock all predicates as system predicates. If
development, save the predicates in their current state and keep reading resources from their source (if present). See also resource/3.
true(default), run autoload/0 first.
save(default) to save the current operator table or
standardto use the initial table of the emulator.
true, the emulator is the first part of the state. If the emulator is started it will test whether a boot file (state) is attached to the emulator itself and load this state. Provided the application has all libraries loaded, the resulting executable is completely independent of the runtime environment or location where it was built. See also section 22.214.171.124.
save, include shared objects (DLLs) into the saved state. See current_foreign_library/2. If the program strip is available, this is first used to reduce the size of the shared object. If a state is started, use_foreign_library/1 first tries to locate the foreign resource in the executable. When found it copies the content of the resource to a temporary file and loads it. If possible (Unix), the temporary object is deleted immediately after opening.174This option is experimental and currently disabled by default. It will become the default if it proves robust.
This predicate is used by qsave_program/[1,2] to ensure the saved state does not depend on availability of the libraries. The predicate autoload/0 examines all clauses of the loaded program (obtained with clause/2) and analyzes the body for referenced goals. Such an analysis cannot be complete in Prolog, which allows for the creation of arbitrary terms at runtime and the use of them as a goal. The current analysis is limited to the following:
The analysis of meta-predicate arguments is limited to cases where the argument appears literally in the clause or is assigned using =/2 before the meta-call. That is, the following fragment is processed correctly:
..., Goal = prove(Theory), forall(current_theory(Theory), Goal)),
But, the calls to prove_simple/1 and prove_complex/1 in the example below are not discovered by the analysis and therefore the modules that define these predicates must be loaded explicitly using use_module/1,2.
..., member(Goal, [ prove_simple(Theory), prove_complex(Theory) ]), forall(current_theory(Theory), Goal)),
It is good practice to use gxref/0 to make sure that the program has sufficient declarations such that the analaysis tools can verify that all required predicates can be resolved and that all code is called. See meta_predicate/1, dynamic/1, public/1 and prolog:called_by/2.