CSE 341 - Programming Languages

We're using SWI Prolog, version 7.6.4.

When you start Prolog, you should see an introductory greeting and then the Prolog command prompt:

Welcome to SWI-Prolog .....
?- 

Running Prolog on attu

If you're planning on loading a file, it will simplify things to first navigate to the directory that contains your file, so that Prolog can find it easily.

Run Prolog from the command line using

swipl

You can also give a command line argument with a file to be loaded, for example

swipl basics.pl 

Running Prolog on the CSE Undergrad Windows Machines

Run Prolog from the “Start” menu. It's here:
All Programs / DEV TOOLS & LANGUAGES / SWI-Prolog

If you want to load a file, you'll either need to specify an absolute file path, or change the current working directory to the appropriate place. Here's how to change the current working directory. If your files are in your home directory on the Z drive in the cse341 subdirectory, type this at the Prolog command prompt:

working_directory(X, 'Z:\\cse341').

(The double backslash is needed because a single backslash indicates some special character, e.g. \n for newline. And in case you're wondering, X will be unified with the previous working directory.)

Double-clicking on a .pl Prolog source file is going to start perl, so that's not going to work.

Running Prolog on a Personal Machine

SWI Prolog is available for Windows, Mac, and Linux. Here's the download page: http://www.swi-prolog.org/Download.html.

Additional Macintosh hints: if you use the Finder and double-click on SWI Prolog in Applications, depending on your security settings, you may get an error. If you do, try right-clicking (or control-clicking) on the application instead, and say “run it anyway”. You can also run it from the command line using the swipl executable in /Applications/SWI-Prolog.app/Contents/MacOS, if you installed it in the default location and add this to your path. swipl will give a warning: “Cannot read termcap database; using dumb terminal settings.” If you can put up with having your terminal insulted every time you run Prolog, you can probably ignore this. To use the graphical debugger, install xquartz (X11), then open a X11 terminal, and run Prolog from there.

Basic Prolog Commands

A few essential commands:

halt.

exit Prolog (short form: control-d)

consult(filename).

load the file named filename.pl (note that if you don't put quotes around the file name, it should be just the name without its .pl extension). If you need some more complex name (for example with a path), put it in single quotes, for example consult('/Users/schmertzkopf/squid.pl').

[filename].

shorthand for consult

help(topic) or apropos(topic).

Brings up the relevant section of the manual in a separate window (so requires X for linux/Mac).

Editing Prolog Code

Prepare source files using any convenient editor. The standard file extension for Prolog files is .pl

If you want to use emacs, include this in your .emacs file in your home directory:

(setq auto-mode-alist
  (cons (cons "\\.pl" 'prolog-mode)
     auto-mode-alist))

There are other versions of emacs Prolog mode if you want to try one - see e.g. Using SWI-Prolog with GNU-Emacs. However, the default mode should be fine for 341.

Debugging

SWI Prolog provides two interfaces to the debugger: a text-based and a graphical interface:

• Overview of the debugger
• The graphical debugger

For old-school debugging use the write goal. For example, here it is in the body of a rule:

notworkingyet(A) :- 
   complicated(A), 
   write('the result after calling complicated is: \n'), write(A),
   yetmorecomplicated(A).