SWI-Prolog does not enforce the use of a particular editor for
writing down Prolog source code. Editors are complicated programs that
must be mastered in detail for real productive programming and if you
are familiar with a specific editor you should not be forced to change.
You may specify your favourite editor using the Prolog flag editor,
the environment variable
EDITOR or by defining rules for
prolog_edit:edit_source/1 (see section
The use of a built-in editor, which is selected by setting the Prolog
flag editor to
has advantages. The XPCE editor object around which the built-in
PceEmacs is built can be opened as a Prolog stream allowing analysis of
your source by the real Prolog system.
central predicate for editing something is edit/1,
an extensible front-end that searches for objects (files, predicates,
modules as well as XPCE classes and methods) in the Prolog database. If
multiple matches are found it provides a choice. Together with the
built-in completion on atoms bound to the
TAB key this
provides a quick way to edit objects:
?- edit(country). Please select item to edit: 1 chat:country/10 '/staff/jan/lib/prolog/chat/countr.pl':16 2 chat:country/1 '/staff/jan/lib/prolog/chat/world0.pl':72 Your choice?
One of the nice features of Prolog is that the code can be modified while the program is running. Using pure Prolog you can trace a program, find it is misbehaving, enter a break environment, modify the source code, reload it and finally do retry on the misbehaving predicate and try again. This sequence is not uncommon for long-running programs. For faster programs one normally aborts after understanding the misbehaviour, edit the source, reload it and try again.
One of the nice features of SWI-Prolog is the availability of make/0, a simple predicate that checks all loaded source files to see which ones you have modified. It then reloads these files, considering the module from which the file was loaded originally. This greatly simplifies the trace-edit-verify development cycle. After the tracer reveals there is something wrong with prove/3 , you do:
Now edit the source, possibly switching to other files and making
multiple changes. After finishing invoke make/0,
either through the editor UI (Compile/Make (
Control-M)) or on the top-level and watch the files being
reloaded.15Watching these files is
a good habit. If expected files are not reloaded you may have forgotten
to save them from the editor or you may have been editing the wrong file
?- make. % show compiled into photo_gallery 0.03 sec, 3,360 bytes