hermit_type.zig

pub fn HermitType(comptime S: type, comptime T: type) type {
    return struct {
        pub const State = S;
        pub const Out = T;

        pub const Event = State;

        pub const Action = struct {
            state: State,
            value: ?Out,

            pub inline fn _return(state: State, out: Out) Action {
                return .{ .state = state, .value = out };
            }

            pub inline fn _continue(state: State) Action {
                return .{ .state = state, .value = null };
            }
        };

        pub const Next = fn (event: Event) Action;

        pub const Deinit = fn (state: State) void;

        pub fn nop(_: State) void {}

        pub inline fn run(state: State, comptime next: Next, comptime deinit: Deinit) Out {
            var a = Action._continue(state);
            defer deinit(a.state);
            const a_i = .always_inline;
            while (a.value == null) a = @call(a_i, next, .{a.state});
            return a.value.?;
        }
    };
}