Some of the built-in predicates provided by SWI-Prolog, such as
is/2, are implemented in C and included as native functions in
the SWI-Prolog runtime. It is sometimes useful to examine the
implementation of such native built-in predicates by reading its
definition in the SWI-Prolog C sources. Sweep knows about SWI-Prolog
native built-ins, and can find and jump to their definitions in C when
the user has the SWI-Prolog sources checked out locally.
Location of the SWI-Prolog source code root directory.
The way Sweep locates the SWI-Prolog sources depends on the user
option sweeprolog-swipl-sources. Setting it to nil
disables searching for definitions of native built-ins altogether. To
point Sweep to the root directory of the SWI-Prolog source code, set
sweeprolog-swipl-sources to the name of that directory. Any
non-nil non-string value says to try and locate a checkout of
the SWI-Prolog sources among known project root directories (Sweep
consults Emacs’s built-in project-known-project-roots to find
your project roots, see (emacs)Projects).
With sweeprolog-swipl-sources set, the provided commands for
finding predicate definitions operate seamlessly on native built-ins
to display their C definitions. These commands include:
xref-find-definitions) in Sweep Prolog mode buffers
(see Definitions and References), and
help-view-source) in the *Help* buffer produced
by M-x sweeprolog-describe-predicate (see Prolog Help).