Language basics

// Purpose: the core of the language in one place — constants, records,
// enums, functions, loops, match, Option and Result with `?`.
// Category: pure
// Permissions: none
// Side effects: none
// Run: t0 run examples/11_language_basics.tz

lang ">=0.1.1, <0.2.0";

const TAKER_FEE: Ratio = bps(5);

struct Order {
    side: Direction,
    size: Quantity,
    limit: Option<Price>,
}

enum Direction {
    Buy,
    Sell,
}

fn sign(side: Direction) -> Int {
    return match side {
        Direction.Buy => 1,
        Direction.Sell => -1,
    };
}

/// Net position after a list of orders, in units.
fn net(orders: List<Order>) -> Quantity {
    let mut total = qty(0);
    for o in orders {
        if sign(o.side) > 0 {
            total = total + o.size;
        } else {
            total = total - o.size;
        }
    }
    return total;
}

fn fee_of(o: Order) -> Result<Money, Error> {
    if o.limit.is_none() {
        return Err(error("E-NO-LIMIT", "a market order has no price to charge a fee on yet"));
    }
    let limit = o.limit.expect("checked above");
    return Ok(limit * o.size * TAKER_FEE);
}

fn total_fees(orders: List<Order>) -> Result<Money, Error> {
    let mut total = money(0, USDT);
    for o in orders {
        total = total + fee_of(o)?;
    }
    return Ok(total);
}

fn main() {
    let orders = [
        Order { side: Direction.Buy, size: qty(0.5), limit: Some(price(64000, USDT)) },
        Order { side: Direction.Sell, size: qty(0.2), limit: Some(price(64500, USDT)) },
    ];
    print("net " + to_string(net(orders)));
    print(total_fees(orders));
    let mut with_market = orders;
    with_market.push(Order { side: Direction.Buy, size: qty(1), limit: None });
    match total_fees(with_market) {
        Ok(fees) => print(fees),
        Err(e) => print("refused: " + e.code),
    }
    let mut countdown = 3;
    while countdown > 0 {
        countdown = countdown - 1;
    }
    print("countdown " + to_string(countdown));
}
// expect-output: net 0.3
// expect-output: Ok(22.45000 USDT)
// expect-output: refused: E-NO-LIMIT
// expect-output: countdown 0