const std = @import("std");

const warn = std.debug.warn;
const allocator = std.debug.global_allocator;

fn foo(n: u32) void {
    warn("{} * 2 = {}\n", n, n * 2);
}

pub fn main() !void {
    var is_finished: bool = false;

    var handle = try async<allocator> slow_action(&is_finished);

    var mapped = try async<allocator> map(u32, void, handle, foo, &is_finished);

    while(!is_finished) {
        resume mapped;
    }

    cancel mapped;
}

async fn map(comptime T: type, comptime U: type, p: promise-> T, f: fn(T) U, is_finished: *bool) void {
    while(!is_finished.*) {
        resume p;
    }

    var result = await p;

    f(result);

}

async fn slow_action(is_finished: *bool) u32 {
    suspend;
    var n: usize = 0;

    while(n < 10): (n += 1) {
        suspend;
    }

    is_finished.* = true;
    return 10;
}