jProlog was written by Bart Demoen and Paul Tarau.
==================================================
Basically, we wanted to learn Java :-)
That's visible from the code. But we believe we made some good choices
for instance wrt representation of heap objects.
It works in java version "1.0.2"

Speed of execution was never our concern, but we were nicely surprised
by the speed with which is was possible to add exotic features to the
basic implementation.
BTW, there is no interface (yet) to Netscape or JDK appletviewer,
it is standalone without GUI.

Sample session
--------------

java -cs Prolog
jProlog 0.1 Copyright (C) Bart Demoen, Paul Tarau 1996
?- ap([1,2],[3],X) .
X = [1,2,3]



exit with ?- halt . or ^D


Set your
--------
CLASSPATH=/home/java/JDK-1.0.2/lib/classes.zip:X

X stands for the concatenation of the directories where the (compiled)
Prolog programs (a bunch of pred_*.class files) are and where this
Prolog-in-Java system is installed.


To use the Prolog to Java compiler
----------------------------------

You need a Prolog system (SICStus, BinProlog, BIMprolog are ok - SWI
doesn't work apparently - for info on freely available BinProlog,
contact Paul Tarau: taraup@umoncton.ca)

To compile a Prolog file to Java:

	prolog comp
	?- comp(file) .


Before you can start up the system
----------------------------------

Some files need to be compiled:

	javac Prolog.java
	javac builtins.java

(in this order)

and also the Prolog files

	someprolog
	read.pl

What this implementation has
----------------------------
Too much to enumerate :-)
It is close to Clocksin-Mellish Prolog, with lots of the typical builtins.
It runs some famous benchmarks happily (and slow :-) like boyer
(slightly adapted because this implementation doesn't deal with if-then-else).

It also has

	intuitionistic assumption (assume/2)
	backtrackable destructive assignment (setarg/3)
	delayed execution (freeze/2)

It loads predicates on need, similar in spirit to what Java does itself.

And it has a garbage collector of course: we inherited it from Java !


The things that are missing in this implementation
--------------------------------------------------
The compiler generates very naive code:
	no indexing
	no specialisation of unification
	(almost) no inlining of simple builtins
Some missing builtins: I/O has only read/1, write/1 and nl.
Read/1 is very slow, because in Prolog and a backtracking parser.
No floating point numbers/strings.
No error handling as in ISO Prolog.
Does not deal with the if-then-else ( -> ;).
Most notably: there is no consult/1 predicate ! See above.
Documentation is missing completely.


If you have
-----------
comments about the implementation, what you liked or disliked, questions,
suggestions or plans to do work on this yourself, please let us know

Recent additions
----------------

1. Calling Prolog from Java - latest change: Wed Feb  5 15:13:56 EST 1997

Several people asked how to call Prolog from within a Java program.
In file PrologFromJava.java (replacing Prolog.java - sorry for the
names) you will find a way how it can be done: it is just one way,
if you have requests, please let me know ("me" = Bart - I haven't
had time to look at what Paul has done in this respect, but it will
soon happen :-)
There is more documentation in docPrologFromJava.


Bart Demoen Bart.Demoen@cs.kuleuven.be
Paul Tarau taraup@umoncton.ca