VALGOL I INFORMATION
		--------------------		G. A. Edgar

This file contains a description of the language VALGOL I, a
(very) small derivative of ALGOL-60.  It is intended to
explain the compiler VALGOL.PRO on this disk.

This language was published in a paper by D. V. Schorre
in 1964 as a sample language for META II.  His paper was
reprinted in Dr. Dobb's Journal, April, 1980.

First, we will go through a description of the language.
Then we will take a sample file and see what is involved in
getting it to run.

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

VALGOL I is basically a subset of ALGOL-60.  The main
peculiarities are these:
     (1)  The key words that are usually typeset in boldface
are preceded by a period.  ( .begin .end .if .then .else .until

comparing two expressions.  ( .= )
     (2)  There is only one data type, namely .integer .
This is a 16 bit two's-complement number in the compiler
supplied. Thus you go from 0 up to 65535, and then back to 0.
     (3)  The assignment statement is reverse from the normal
order.  (  5 =: x  assigns the value 5 to x )
     (4)   Arithmetic allows addition ( + ) subtraction ( - )
and multiplication ( * ) .  There is no unary minus sign,
so if you want -2 you can write either 0-2 or else 65534 (or,
for that matter, 196606) .

Let's walk through some of the syntax of the language.

A program consists of the keyword ".begin", 
followed by an optional declaration, followed by one or more
statements, separated by semicolons ( ; ) , followed by the
keyword ".end".

A declaration consists of the keyword ".integer" followed
by a list of identifiers, separated by commas.

A statement is one of the following:

(1) an I/O statement.  This is either of the form
     edit( expression , 'string')
which will send (expression) spaces and then the (string) to
the console, or of the form
     print
which will send an end-of-line to the console.

(2) an assignment statement, which has the form
     expression =: variable

(3) a loop, of the form
     .until expression .do statement
A value of 0 for the expression is considered false, and a
nonzero value is true.

(4) a conditional statement of the form
     .if expression .then statement .else statement
The .else is not optional.

(5) a block, which consists of the keyword ".begin",
followed by an optional declaration, followed by zero
or more statements, separated by semicolons, followed by the
keyword ".end".  Notice that the null statement in the form
     .begin .end
is allowed.  It is important that the semicolon is a
statement separator, and not a statement terminator (as in
some other languages, such as PL/I and C).  You will get
a syntax error message if you put a semicolon just before
the ".end" in a block.

A test for equality is allowed:
    2 + x .= y * y
This has value 1 if true and 0 if false.  Expressions can be
built up from variables, numbers, the operations + , - ,
*, and parentheses "(" , ")".


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

Now we will go through a compile and run of a VALGOL program.

Let's use this sample program:



0 =: x ;

	.begin
	edit ( 1 + 14*x - x*x , '+' ) ;
	print ;
	x + 1 =: x
	.end


Suppose it is in a file called P.VAL.  We compile it:

B>EPRO

E-Prolog   ver. 2.3      (August 1, 1985)
> (LOAD VALGOL)

> (compile P)
VALGOL 1 compiler - translates VALGOL to ASM
P.VAL -> P.ASM

*** Compilation complete ***
Yes.
> ^C

This creates an ASM-compatible assembly-language file that
begins like this:

VBDOS	EQU	5
VTPA	EQU	256
VCR	EQU	13
VLF	EQU	10
	ORG	VTPA
	LXI	SP,VSTACK
	JMP	V1
Vx:	DW	0
V1:
	LXI	H,0
	SHLD	Vx
V2:
	LHLD	Vx
	PUSH	H
	LXI	H,9
	...
and so on.

Next, the program can be compiled and run as normal:

B>ASM P.BBZ

CP/M ASSEMBLER - VER 2.0
01F5
001H USE FACTOR
END OF ASSEMBLY

B>LOAD P


FIRST ADDRESS 0100
LAST  ADDRESS 01B8
BYTES READ    00B7
RECORDS WRITTEN 02

B>P
 +
               +
                         +
                                  +
                                        +
                                              +
                                                 +
                                                  +
                                                 +
                                              +
                                        +
                                  +
                         +
               +
 +

And there it is.


-------------------------------
G. A. Edgar

	May 21, 1984     [CompuServe release]
revised October 21, 1984 [for Meta4 material, SIG/M vol. 208]
revised August 1, 1985   [for E-Prolog release]