POPEYE - A Linear Logic Programming Language that
         Translates to Java

Authors
-------
	Dale Miller and Alex Betis
	
	Mostly worked on this during Summer and Fall 1999
	The Language and its foundations are exposed in
	details in Alex's Master's Thesis, available for
	download at http://www.cse.psu.edu/~dale/betis/

Current distribution
--------------------

	Requirements
	------------	

	You need a working version of SML of New Jersey, with	
	the Terzo Lambda Prolog distribution built onto it.
	
	This distribution, as well as instructions on how to
	install it, are available at http://www.cse.psu.edu/~dale/

	Modules
	-------

	The Popeye system makes use of the following modules:

	popeye.sig 	: 	Signature file for the Popeye language
	java.sig	: 	Signature file for some Java-specific
				commands.
	interp.mod 	:	Interpreter for the language	
	tchecker.mod	:	Type-inferer/checker for the language
	spinach.mod	:	Java code generator

	For running the interpreter, only the first three files are
	needed. For the typeckecker, the first four. For the Java
	code generator, all of them must be loaded in Terzo.

	We also provide examples. The trivial switch is given in:

	switch.pop.mod  : 	Switch example

	This file must also be loaded in Terzo if we want to use
	switches in the system. Usually, though, each object foo
        is represented by three (and not only one) files.

		- The foo.pop.sig contains the Lambda Prolog 
		  signature of the object
		- The foo.pop.mod contains the code for the
		  object
		- The foo.pop.spi contains the type-checking 
		  rules and the code generation rules.
	
	We provide the following objects (which are all detailled
	in the MS Thesis):

	cell.pop.*	: 	A simple cell to be put into a queue
	queue.pop.*	:	A FIFO queue using cells

	wire.pop.*	: 	An object representing an electrical
				wire.
	gate.pop.*	: 	An abstract mother class for logical
				gates.
	unigate.pop.*	:	An abstract mother class for logical
				gates with only one input. Inherits
				gate.pop.*.
	bigate.pop.*	:	An abstract mother class for logical
				gates with two inputs. Inherits
				gate.pop.*.
	notgate.pop.*	: 	A NOT gate object. Inherits unigate.pop.*
	andgate.pop.*	:	A AND gate object. Inherits bigate.pop.*

	Finally, we provide a few starters to automate the load process
	in Terzo.

	go		: 	#load all the files related to logical
				gates as well as those needed for
				the system to work (that is, all the
				base Popeye modules).
	qgo		: 	Same as above but for the queue object.

Examples
--------

	Interpreter
	-----------

	This is a few examples of what can be done in the interpreter.	
	
		With the queue
		--------------

		#query queue, cell, queuespi, cellspi, interpreter, typechecker, spinach.
		?- interp nil nil (new queue q\ enqueue q (pint 1)) end.
		
		solved
		?- interp nil nil (new queue q\ enqueue q (pint 1) >> enqueue q (pint 2) >> 
                dequeue q C) end.

		C = pint 1; 

		no more solutions.
		?- interp nil nil (new queue q\ enqueue q (pint 1) >> enqueue q (pint 2) >> 
		dequeue q C >> dequeue q D ) end.
	
		C = pint 1
		D = pint 2;

		no more solutions.
		?- tcheck nil queue nil tmod nil.
		loc context
		prog
		clause
		t-check
		empty
		prog
		pi pi clause
		t-check
		t-check
		.
		.
		.
		t-check
		t-check
		t-check
		t-check
		branch
		branch
		t-check

		solved
		?- spinach nil nil queue Java.
		clause
		t-check
		empty
		.
		.
		.
		branch
		branch
		t-check
		!!!!!!!!!!!!!!!
		Java =
		 "public class Queue extends Object{
		Cell head;
		Queue(){
		.
		.
		.
		obj=newQ.dequeue();}
		}
		return obj;
		}
		}
		"
		
		?- 

		With the gates
		--------------

		#query list, listspi, gate, gatespi, unigate, unigatespi, notgate, notgatespi,
		bigate, bigatespi, andgate, andgatespi, interpreter, typechecker, spinach.
		?- interp nil nil ( new wire a\ new wire b\ new wire c\ new andgate a b c g\
		set_signal a (pcst wire on) >> set_signal b (pcst wire off) >> get_state g S) end.
	
		S = (pcst wire off)

		?-

		Of course, what can also try backtracking but it made my Celeron explode.

		Typechecker and Spinach are used in a similar fashion to the queue.

		?- tcheck nil andgate nil tmod nil.
		.
		.
		.
		solved

		?- spinach nil nil andgate Java.

		Java = 
		.
		.
		.		
		solved

Additionnal stuff
-----------------

	We put the java code generated with some testing code in the java/ 
	subdirectory. You need Java 1.7 and higher to compile the code.

	The code for the Prolog-like list object in Java (PopList.java)
	was not generated but hand-written, for the motives exposed
	in the "examples" section of the thesis. It was tested but
	is not considered optimum. Its coding was necessary for the
	logical gates example to work.


TO DO
-----

	This work is very alpha, very fault-intolerant and 
	as a consequence requires a lot of tolerance from 
	the potential user. :) An effort should be made
	to provide a better environment for all this.

	A better parser for the language
	
	Automatic .spi file generation or "on-the-fly" extraction
	
	Lots o' stuff... (See MS thesis)



					Alex - 20/01/00