Monty Interpreter

INTRODUCTION

Monty 0.98 is a scripting language that is first compiled into Monty byte codes. It relies on a unique stack with specific instructions to manipulate it. By convention, the files containing Monty bytecodes have the .m extension. There is no more than one instruction per line and there can be any number of spaces before or after the opcode and its argument.

Monty byte code file

Monty byte code files can contain blank lines (empty or made of spaces only and any additional text after the opcode or its required argument is not taken into account:

musangi@ubuntu:~/monty$ cat -e testfiles/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        $
$
pall This is the end of our program. Monty is awesome!$
musangi@ubuntu:~/monty$

The Monty program

• Usage: monty file
  • where file is the path to the file containing Monty byte code
• If the user does not give any file or more than one argument to your program, print the error message USAGE: monty file, followed by a new line, and exit with the status EXIT_FAILURE
• If, for any reason, it's not possible to open the file, the program prints the error message Error: Can't open file , followed by a new line, and exit with the status EXIT_FAILURE
  • where is the name of the file.
• If the file contains an invalid instruction, the program prints the error message L<line_number>: unknown instruction , followed by a new line, and exit with the status EXIT_FAILURE
  • where <line_number> is the line number where the instruction appears.
  • Line numbers always start at 1.
• The monty program runs the bytecodes line by line and stop if either:
  • it executed properly every line of the file.
  • it finds an error in the file.
  • an error occured
• If the program can't malloc anymore, the error message Error: malloc failed is printed, followed by a new line, and exit with status EXIT_FAILURE.
• Only malloc and free are used to manage heap memory.

OPCODES AND FUNCTIONS

OPCODE	FUNCTION	Usage
push	Pushes an element to the stack.	push
pall	Prints all the values on the stack starting from the top of the stack	pall
pint	Prints the value at the top of the stack, followed by a new line.	pint
pop	Removes the top element of the stack.	pop
swap	Swaps the top two elements of the stack.	swap
add	Adds the top two elements of the stack. The result is stored in the second element. The list is one element short.	add
nop	Does nothing	nop
sub	Subtracts the top element of the stack from the second top element of the stack. The result is stored in the second element. The list is one element short.	sub
div	Divides the second top element of the stack by the top element of the stack. . The result is stored in the second element. The list is one element short.	div
mul	Multiplies the second top element of the stack with the top element of the stack. The result is stored in the second element. The list is one element short.	mul
mod	Computes the rest of the division of the second top element of the stack by the top element of the stack. The result is stored in the second element. The list is one element short.	mod
pchar	Prints the char at the top of the stack. Integer is treated as the ascii value of the character to be printed.	pchar
pstr	Prints the string starting at the top of the stack. Integer is treated as the ascii value of the character to be printed. The string stops when either The stack is over. The value of the element is 0. The value of the element is not on the asci table. If the stack is empty, a new line is printed.	pstr
rotl	Rotates the stack to the top. The top element of the stack becomes the last one. The second top element of the stack becomes the first one. rotl never fails.	rotl
rotr	Rotates the stack to the bottom. The last element of the stack becomes the top element of the stack rotr never fails.	rotr

OPCODE ERRORS AND EXIT CODES

OPCODE	ERROR	CAUSE OF ERROR	EXIT CODE
push	L<line_number>: usage: push integer	Argument passed is not an integer or was not passed	EXIT_FAILURE
pall	nothing is printed	empty stack	none
pint	L<line_number>: can't pint, stack empty	empty stack	EXIT_FAILURE
pop	L<line_number>: can't pop an empty stack	empty stack	EXIT_FAILURE
swap	L<line_number>: can't swap, stack too short	stack has less than 2 elements	EXIT_FAILURE
add	L<line_number>: can't add, stack too short	stack has less than 2 elements	EXIT_FAILURE
sub	L<line_number>: can't sub, stack too short	stack has less than 2 elements	EXIT_FAILURE
div	L<line_number>: can't div, stack too short	stack has less than 2 elements	EXIT_FAILURE
	L<line_number>: division by zero	top element of the stack is 0	EXIT_FAILURE
mul	L<line_number>: can't mul, stack too short	stack hass less than 2 elements	EXIT_FAILURE
mod	L<line_number>: can't mod, stack too short	stack hass less than 2 elements	EXIT_FAILURE
	L<line_number>: division by zero	top element of the stack is 0	EXIT_FAILURE
pchar	L<line_number>: can't pchar, value out of range.	the integer value is not in the ascii table.	EXIT_FAILURE
	L<line_number>: can't pchar, stack empty.	stack is empty	EXIT_FAILURE

AUTHOR

Silvia Musangi