SWI-Prolog does not enforce the use of a particular editor for
writing Prolog source code. Editors are complicated programs that must
be mastered in detail for real productive programming. 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.
The use of a built-in editor, which is selected by setting the Prolog
flag editor to pce_emacs,
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.
The
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 '/home/jan/.config/swi-prolog/lib/chat/countr.pl':16
2 chat:country/1 '/home/jan/.config/swi-prolog/lib/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 will normally abort 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. For example, after the tracer
reveals there is something wrong with prove/3 , you do:
?- edit(prove).
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-C
Control-M)) or on the top level, and watch the files being
reloaded.43Watching 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
(wrong directory).
?- make.
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