A trivial sample exploring the envelope budgeting method in OCaml

budget.ml

open Printf

type envelope = {
	name: string;
	amount: int;
}

type account = { 
	name: string; 
	balance: int;
	envelopes: envelope list;
}

let open_account amt = 
	let envs = [{name = "available"; amount = amt}] in
	{ name = "current"; balance = amt; envelopes = envs}

let deposit acc envname amt =
	let envs = acc.envelopes |> List.map (fun (e: envelope) -> 
		match e with 
		| x when x.name = envname -> { x with amount = x.amount + amt} 
		| _ -> e
	) in
	let total = envs |> List.map (fun e -> e.amount) |> List.fold_left(fun x y -> x + y) 0 in
	{ acc with balance = total; envelopes = envs }

let print_status (acc: account) =
	printf "envelopes:\n";
	acc.envelopes |> List.iter (fun (e: envelope) -> printf "%s - %d\n" e.name e.amount);
	printf "total: %d\n\n" acc.balance

let add_envelope acc (env: envelope) =
	if acc.envelopes |> List.filter(fun (e: envelope) -> e.name = env.name) |> List.length > 0 then raise (Failure (env.name ^ " envelope already exists!"));
    let envs = env::acc.envelopes in
    let total = envs |> List.map(fun e -> e.amount) |> List.fold_left(fun x y -> x + y) 0 in
    { acc with envelopes = envs; balance = total }

main.ml

open Account

let acc = open_account 100;;
print_status acc;;

let acc = add_envelope acc { name = "savings"; amount = 25 };;
print_status acc;;

let acc = deposit acc "available" 50;;
print_status acc;;

let acc = add_envelope acc { name = "loans"; amount = 325 };;
print_status acc;;