5 Prolog Initialization and Cleanup ¶

The embedded SWI-Prolog runtime must be initialized before it can start executing queries. Normally, Sweep takes care of initializing Prolog for you the first time you use a command that requires running some Prolog code. This section elaborates about Prolog initialization and its customization options in Sweep:

User Option: sweeprolog-init-args ¶

List of strings used as initialization arguments for Prolog. Sweep uses these as the args argument of sweeprolog-initialize when it initializes Prolog on-demand.

Sweep loads and initializes Prolog on-demand at the first invocation of a command that requires the embedded Prolog. The user option sweeprolog-init-args says which arguments to pass to Prolog initialization. Its value is a list of strings that you can extend if you want to pass specific command line flags SWI-Prolog. For example, to limit the embedded Prolog stack to 512 MB, add the following to your Emacs configuration:

(with-eval-after-load 'sweeprolog
  (push "--stack-limit=512m" sweeprolog-init-args))

Sweep initializes Prolog from Elisp by calling function sweeprolog-initialize.

Function: sweeprolog-initialize prog &rest args ¶

Initialize the embedded Prolog runtime. prog should be the path to the swipl executable, and args should be a list of command line arguments for swipl. Sweep initializes Prolog as if it was started from the command line as prog args.

The function sweeprolog-initialize takes one or more string arguments and initializes the embedded Prolog as if it were invoked externally in a command line with the given strings as command line arguments, where the first argument to sweeprolog-initialize corresponds to argv[0]. This function is implemented in C in sweep-module (see High-level Architecture).

It is also possible to specify initialization arguments to SWI-Prolog by passing them as command line arguments to Emacs, which can be convenient when using Emacs and Sweep as an alternative for the common shell-based interaction with SWI-Prolog. This is achieved by adding the flag --swipl-args followed by any number of arguments intended for SWI-Prolog, with a single semicolon (;) argument marking the end of the SWI-Prolog arguments, after which further arguments are processed by Emacs as usual (see (emacs)Emacs Invocation for more information about Emacs’s command line options), for example:

emacs --some-emacs-option --swipl-args -l foobar.pl \; --more-emacs-options

In order for Sweep to be able to handle Emacs’s command line arguments, you must call sweeprolog-handle-command-line-args before Emacs processes the --swipl-args argument.

Function: sweeprolog-handle-command-line-args ¶

Enable support for the Sweep-specific --swipl-args Emacs command line flag. This flag can be used to specify additional Prolog initialization arguments for Sweep to use when initializing Prolog on-demand, directly from Emacs’s command line invocation.

This function makes Emacs recognize the --swipl-args command line flag by adding a dedicated handler function to command-line-functions (see (elisp)Command-Line Arguments). If you want to use --swipl-args, you should arrange for command-line-functions to run before Emacs processes --swipl-args. To do that, either place a call sweeprolog-handle-command-line-args in your Emacs configuration, or call it from the command line right before --swipl-args:

emacs -f sweeprolog-handle-command-line-args --swipl-args -l foobar.pl \;

Command: sweeprolog-shutdown ¶

Shut down the embedded Prolog runtime.

Command: sweeprolog-restart ¶

Restart the embedded Prolog runtime.

The command sweeprolog-shutdown shuts down the Prolog runtime and frees up resources Prolog allocated. You cannot shut down Prolog with running top-levels (see The Prolog Top-level)—if you invoke sweeprolog-shutdown while you have running top-levels, this command suggests killing them, and if you refuse it complains and keeps Prolog running. The command sweeprolog-restart is similar to sweeprolog-shutdown, expect it starts the embedded Prolog runtime anew after shutting it down. When you invoke sweeprolog-restart with a prefix argument (C-u M-x sweeprolog-restart RET), this command prompts for additional initialization arguments to pass to the embedded Prolog runtime when restarting it.