A Monty Bytecode Interpreter

Background:

Monty is a scripting language that is compiled into bytecodes and the purpose of this interpreter is to execute the files containing the bytecode.

Program Execution:

This interpreter parses the .m files line by line and executes commands from the opcodes in the file until it hits an error.

Running the program

1. compile with gcc version 4.8.4 gcc -Wall -Wextra -Werror -pedantic *.c

2. ./executable path/to/.m/file e.g. ./a.out test.m

Command Execution

1. If an opcode takes an argument, anything after the opcode and its argument is ignored.
2. If an opcode doesn't take an argument and an argument has been entered, it is ignored.
3. As commands are being parsed by the interpreter, any number of tabs and spaces is ignored and the opcode is executed.
4. If an error condition has been met, then the interpreter will display an error on the stderr including the line number and exit with the EXIT_FAILURE macro.
5. If an opcode was spelled incorrectly, then the program returns error code 4 and exits with EXIT_FAILURE.

The format of the stderr message is shown below for reference.

List of implemented opcodes:

Opcode	Functionality	Usage	Error Code
push	pushes an element to the stack	push <int> where <int> is an integer. Push fails if the argument is not an integer or no argument is given at all.	5
pall	prints all the values on the stack	If there isn't anything on the stack, it doesn't print anything.	None
pint	prints the value at the top of the stack	pint	10
pop	removes the top element of the stack	pop	11
swap	swaps the top 2 elements of the stack	swap	12
add	adds the top 2 elements of the stack, stores it in the second element of the stack, and pops the stack	add	13
nop	doesn't do anything	nop	None
sub	subtracts the top 2 elements of the stack, stores it in the second element of the stack, and pops the stack	sub	16
div	divides the 2nd element of the stack with the first, stores it in the second element of the stack, and pops the stack	div	14 or 15
mul	multiplies the top 2 elements of the stack, stores the result	mul	17
mod	computes the modulus of the 2 top 2 elements in the stack, stores it in the 2nd element of the stack, and pops the stack	mod	18 or 15
pchar	prints the char at the top of the stack	pchar	19 or 20
pstr	prints the string sitting in the stack from the top of the stack to the bottom using the integers as ASCII values	pstr	None
rotl	rotates the stack to the top, moves the top element of the stack to the bottom and pushes the stack up one	rotl	None

Examples

There are 2 files located in the bytecodes/ directory.

000.m
push 0
push 1
push 2
push 3
pall
push 4
push 5
push 6

pall

output
3
2
1
0
6
5
4
3
2
1
0

001.m
push 0 Push 0 onto the stack
push 1 Push 1 onto the stack

push 2
push 3
pall

push 4
push 5
push 6

output
3
2
1
0

Error Codes:

Error Code	Error Message on stderr
4	unknown instruction
5	usage: push integer
7	Error: malloc failed
8	Error: Can't open file
9	USAGE: monty file
10	can't pint, stack empty
11	can't pop an empty stack
12	can't swap, stack too short
13	can't add, stack too short
14	can't div, stack too short
15	division by zero
16	can't sub, stack too short
17	can't mul, stack too short
18	can't mod, stack too short
19	can't pchar, value out of range
20	can't pchar, stack empty

Error print format

Error 9

fprintf(stderr, "%s\n", error message)

Error 8

fprintf(stderr, "%s %s\n", error message, filename sent to executable)

Error 4

fprintf(stderr, "L%d: %s %s\n", line number, error message, opcode string)

All other error codes

fprintf(stderr, "L%d: %s\n", line number, error message)

Authors

Name	Github Link	Twitter
Brent Janski	https://github.com/talktobrent	https://twitter.com/swcosnow
Hemant Heer	https://github.com/VortexH	https://twitter.com/hemant_heer