COMP204 2008 Assignment Two

This assignment exercises your IO skills.

You are to implement a simple interpreter which
can read and write doubles from a binary file
and do some rudimentary computation.
The actions of the interpreter will be specified
by reading commands from standard input
(think very simple scripting language).
The following grammar defines the syntax
of command lines:

line = OPEN filename | location <= location operator location
operator = + | - | * | / | POWER
location = VARIABLE offset | FILE offset

"OPEN filename" opens the respective file for IO.
It will close any currently open file. So at each
time there will be only one open file. 
"filename" is the name of some binary file containing
only double numbers.
All computation should use double values.
"offset" will be of type "int".
You should use RandomAccessFile to be able to read and write
arbitrary locations inside the binary file.
"FILE offset" designates some position in that file.
You will read from that location (if that location
is used on the right-hand side of the assignment 
operator "<=") or write to that location (if that
location is used on the left-hand side of "<=").
Similar for "VARIABLE", but these values are kept
in memory, i.e. you need to setup some data-structure
to keep track of "VARIABLE"s.
"VARIABLE"s are to be initialized to 0.0.
In addition all lines will print some
feedback to standard output:
OPEN prints "opened <FileName>"
Assignments print location and result,
e.g. "FILE 13 <= 34.2" if location 13 in
the file was assigned 34.2

So assuming binary file "numbers" contains
exactly two binary doubles: 1.0 and 2.0 in
that order, then the following lines

OPEN numbers
VARIABLE 0 <= FILE 0 + FILE 1
FILE 0 <= FILE 1 * VARIABLE 0

would first open file "numbers",
then sum the double values 1.0 and 2.0
(found at positions 0 and 1) to 3.0 and
assign that value to "VARIABLE" 0.
Third step computes 2.0 * 3.0
(file position 1 times variable 0)
and save that value as the new first
value in file "numbers". So after
that numbers would contain 6.0 and 2.0
in that order instead of 1.0 and 2.0.

Due date: Monday, 11th August

What to submit:
One java file containing all your code.
Document your code well.
Use the javadoc @author tag to give your name and ID!