Concurrent Pascal-S Implementation Notes
		========================================

	ALL PROGRAMS SHOULD BE WRITTEN IN lowercase!

	Start CCP by typing    CCP sourcefilename.
        ( i.e CCP DINPHIL.CCP)

	The subset of Pascal compiled is:

	1. simple types : integer, boolean, char.
	2. arrays (may be multidimensional).
	3. strings. just literals in write statements, e.g.
		writeln('Leipzig');
	4. operators:
	     integer : +,-,*, div, mod.
	     boolean : not, and, or.	 
	5. relational operators
	    =, <>, >, <, >=, <=
	6. declarations:
	    const, type, var, procedure, function.
	7. statements:
	   assignment
	   if - then - else
	   if - then -
	   while - do -
	   repeat - until -
	   for - to - do -
   	8. block structure : begin .... end;
	9. concurrency: in the <main> program !
	    cobegin p1; p2; p3;... coend.
	    p1.. must be global procedures (= processes)..
	    on execution of cobegin, all procedures are activated for
	    concurrent execution. The main program continues after coend
	    when all processes are terminated.
	10. wait(s) and signal(s) are standard procedures. They operate on
	    variables of type SEMAPHORE which is handled like an integer.
	    No syntactic protection is provided. Semaphores should be
	    initialized in the main program before any cobegin statement.

BUGS:
	Compiler will hang if source contains upper case characters. Feel
	free to modify the scanner in file COMPILE.PAS to fix that.

				------------------
	Compilation is top-down by recursive descent. Be shure you have the
	{$S+} (recursion on} compiler source code toggle on when compiling 
	the compiler overlay!

	The original source file as printed in Ben-Ari's book was too long to
	compile in a single run (some 2800 lines). Therefore, it has been split
	into four Pascal/MT 'modules' which are linked as overlays :

	CCP.PAS

 	root segment, calls the initialization overlay and  the compiler 
	overlay. If no errors occur, the interpreter overlay is called and 
	execution begins. Otherwise, CCP gives <some> error messages and
	returns to CP/M.
	All compiler tables and the code array  are held in memory; therefore
	you can't expect to compile very large programs.
	
	INIT.PAS

	Enters reserved words and predefined identifiers into the compiler
	tables. 

	COMPILE.PAS

	contains scanner, parser and code generation routines. There is no
	provison for a listing of the generated code, but this could readily 
	be added (maybe another overlay). Anybody interested to write this and 
	a set of macros for M80 to have a full native code compiler ?
	Jerry Holter's article in Byte Sept. 83,p.445
	Add multiple tasks to your communication and control program
	would be a good starting point.
	If somebody does it, let me know.

	INTERPRE.PAS

	contains the interpreter for the extended P-code. Originally, this
	was a huge CASE statement. Because of Pascal/MT limitations on the
	procedure and CASE statement size, it has been split into 4 smaller
	CASE statements contained in the procedures EXEC1..4.
	A random number generator is used for dispatching of processes. It 
	uses reals to generate quasi-random numbers between 0 and 1. As this
	is a slow process and the resulting real is converted into an integer
	anyway, this could be improved.
	The constant PMAX contains the maximum number of concurrent processes
	minus one (the main program also is a process). If you change it, you 
	will have to  compile the root too and re-link >ALL< overlays, because
	the root segment's symbol table (CCP.SYM) will change.
	Currently, PMAX is 7.
	If the interpreter stops, a table containing the processes' status
	and a symbolic post mortem dump is displayed.


	Almost all global data is declared in the root segment. This could be
	improved, as a lot of externals result. However, I was too lazy to
	find out which variable is used when & where.

			--------------------

	Other files:

	MAKECCP.SUB

	Submit file for compiling and linking all 4 parts. Could take half an
	hour. I renamed MTPLUS to P, FPREALS to FP, PASLIB to PL, and 
	LINKMT to L. A single overlay area is used, as the overlays do not
	call each other.
	
	Example  programs:

	DINPHIL.CCP

	The classic dining philosophers problem (was it Dijkstra or God
	himself?)

	BOUND.CCP

	The producer-consumer problem with buffersize 1. 

	TRIO.CCP

	three unsynchronized processes writing to the screen. Process 1 writes
	very often; seemingly the random generator is'nt very good (anybody 
	knows a >really< good random number algorithm for 16-bit arithmetic
	(no reals please)?).


EXTRA:

	PLO.PAS

	This is the PL/0 compiler from 

		N. Wirth
		Algorithms + Data Structures = Programs.

	(well, almost.)
	It should compile with Pascal/MT+ v 5.5 to produce PL0.COM.
	RECREAD is a PL/0 sample  program. It reads integer numbers and
	outputs them in the reverse order, if a zero is encountered.
	This compilation also produces a file called RECREAD.MAC, which
	contains the intermediate code generated by PL/0.





  				Happy Deadlock !
		
				Michael Haberler