Data Structures Assignment 1
Due: Aug 10, 5pm
(Submit at moodle.)

Write an interpreter for the following language. Define and use a Procedure class that stores information about one procedure, i.e., the list of its instructions. The instructions are stored parsed: i.e., as < OPERATION-CODE, OPERANDS > tuple. You may choose any representation for op codes (but make sure that you use no literal constant in any of your methods). You need classes Program Instruction, OpCode and Operand. Classed Program and Procedure should each have the execute method that sequentially executes its Instructions. You will also need a VirtualMachine class (that will have your main program) as well as a Parser class. Make sure you handle exceptions (wrong input programs). The execute method for the PRINT instruction may directly call the JAVA print function.
Syntax
COMMENT string
DEFINEPROC procedurename parametername
SET variablename anothervariablename/value
ENDPROC
CALLIF variablename/value procedurename variablename/value
PRINT variablename

Details
All procedures take one input parameter and return no values
The input parameter can only be an integer (of arbitrary size)
All calls are by value
Recursion is allowed
No global variables
Only integer constants -- but of arbitrary width
Each program must have an entry procedure named "start".
CALLIF calls the function if the first operand is non-zero; the last operand provides the parameter value.
Example Code

COMMENT This is a comment
DEFINEPROC recur level
PRINT level
CALLIF level recur level-1
ENDPROC

DEFINEPROC start
SET call 1
CALLIF call recur 3
ENDPROC


Expected Output

3
2
1
0




i don't want the answer ....i just need help understanding the qn....i hv no clue as to what it means and what it wants me to do..

Wow, quite the assignment 1. I have seen this style of program before. What they want you to do is create a series of classes/procedures which when fed instructions in a specific format it calls the appropriate procedure to execute the statement.

So for instance, you read in an instruction like PRINT "hello world" it will read in that line, parse it by knowing the first part is a command and the second part is a parameter. It will then say "Hey, this is a print statement, pass the string 'hello world' to the print procedure" where the print procedure will then print the "hello world" to the screen. But keep in mind that they want the parameters only to be integers (which I am not sure why that is but anyways). It will then move on to the next statement and see that it is a SET command and hand off the variable name along with the value to the SET procedure and that procedure will set the variable with the specified value.

It basically chews through each line and delegates the responsibility to various procedures based on the command and the values of the line.

However if you have questions the best place to ask is the instructor. Don't rely on just my interpretation of this. I would be asking questions too just to get the hang of how the instructor wants the program laid out.



This post has been edited by Martyr2: 3 Aug, 2008 - 09:02 AM