Stack-based VM in OCaml with comparison x86 program

vm.ml

(* Ugly imperative code, meant to be the start of something else - ideally `iter ()` would become `iter ip`. *)

type value = Int of int
  	   | Str of string

type op = Nop
		| Push of value
		| Dup
		| Mul
		| Add
		| Jump of value
		| JumpLT of value * value
		| Call of value

type astack = {mutable values : value list}
let stack = {values=[]}

let push v =
	stack.values <- v :: stack.values

let pop () =
	match stack.values with
		| [] -> failwith "pop on empty stack"
		| x::xs ->
			stack.values <- xs;
			x

let peek () =
	match stack.values with
		| [] -> failwith "peek on empty stack"
		| x::_ -> x

let string_of_value = function
	| Int i -> string_of_int i
	| Str s -> s

let exec program =
	let ip = ref 0 in

	let rec iter () =
		let op = List.nth program !ip in
		(match op with
			| Nop -> ()
			| Push v -> push v
			| Dup -> push (peek ())
			| Add ->
				(match (pop (), pop ()) with
					| (Int rhs, Int lhs) -> push (Int (lhs+rhs))
					| (_, _) -> failwith "invalid operands to add")
			| Mul ->
				(match (pop (), pop ()) with
					| (Int rhs, Int lhs) -> push (Int (lhs*rhs))
					| (_, _) -> failwith "invalid operands to mul")
			| Jump v ->
				(match v with
					| Int addr ->
						ip := addr-1 (* todo: make this more pretty *)
					| _ -> failwith "invalid operand to jump")
			| JumpLT (a, v) ->
				(match (a, v) with
					| (Int addr, Int value) ->
						(match peek () with
							| Int i ->
								if i < value then
									ip := addr-1
							| _ -> failwith "non-int value in JumpLT")
					| _ -> failwith "invalid operand to jump")
			| Call p ->
				(match p with
					| Str "print" -> Printf.printf ": %s\n" (string_of_value (pop ()))
					| _ -> Printf.printf "todo: call %s\n" (string_of_value p)));
		ip := !ip + 1;
		if !ip < List.length program then
			iter ()
	in
	iter ()

let () =
	let program = [Push (Int 0);
				   Push (Int 1);
				   Add;
				   Dup;
				   Push (Int 10);
				   Mul;
				   Call (Str "print");
				   JumpLT (Int 1, Int 10)

	] in
	exec program

x86.s

# I hate my life, that's why I'm writing x86 assembly with AT&T syntax at 6am on a Sunday using only ideone.com

.data
s: .string "%d\n\0"
 
.text
.global main
main:
    xor %eax,%eax
loop:
    movl $1, %ebx
    addl %ebx,%eax
    pushl %eax # add
 
    movl $10,%ebx
    mul %ebx
    pushl %eax # mul
 
    pushl $s
    call printf
    addl $8, %esp
 
    popl %eax # pop add
    cmp $10,%eax
    jl loop
 
        xor     %eax, %eax
        ret