Transforming a function into a generator function

AsyncFibonacci.hx

// original function

function fib():Iterator<Int> {
    var a = 0;
    var b = 1;
    while (true) {
        @yield a;
        b = a + b;
        @yield b;
        a = a + b;
    };
}


// add label 0 (start state) and label -1 (end state)

function fib():Iterator<Int> {
    @section start;
    {
        var a = 0;
        var b = 1;
        while (true) {
            @yield a;
            b = a + b;
            @yield b;
            a = a + b;
        };
    };
    @section end;
    return;
}


// transform var statements

function fib():Iterator<Int> {
    @section start;
    {
        {
            __var_a_1 = 0;
        };
        {
            __var_b_2 = 1;
        };
        while (true) {
            @yield __var_a_1;
            __var_b_2 = __var_a_1 + __var_b_2;
            @yield __var_b_2;
            __var_a_1 = __var_a_1 + __var_b_2;
        };
    };
    @section end;
    return;
}


// transforming control structures

function fib():Iterator<Int> {
    @section start;
    {
        {
            __var_a_1 = 0;
        };
        {
            __var_b_2 = 1;
        };
        {
            @label start_loop;
            @set cond = true;
            if (!@get cond) @goto end_loop;
            {
                {
                    __current = __var_a_1;
                    @state next;
                    return;
                    @label next;
                    @void if (false) null;
                };
                __var_b_2 = __var_a_1 + __var_b_2;
                {
                    __current = __var_b_2;
                    @state next;
                    return;
                    @label next;
                    @void if (false) null;
                };
                __var_a_1 = __var_a_1 + __var_b_2;
            };
            @goto start_loop;
            @label end_loop;
            @void if (false) null;
        };
    };
    @section end;
    {
        @state -1;
        return;
    };
}


// renaming labels and vars

function fib():Iterator<Int> {
    @label start_1;
    {
        {
            __var_a_1 = 0;
        };
        {
            __var_b_2 = 1;
        };
        {
            @label start_loop_3;
            __cond_3 = true;
            if (!__cond_3) @goto end_loop_4;
            {
                {
                    __current = __var_a_1;
                    @state next_5;
                    return;
                    @label next_5;
                    @void if (false) null;
                };
                __var_b_2 = __var_a_1 + __var_b_2;
                {
                    __current = __var_b_2;
                    @state next_6;
                    return;
                    @label next_6;
                    @void if (false) null;
                };
                __var_a_1 = __var_a_1 + __var_b_2;
            };
            @goto start_loop_3;
            @label end_loop_4;
            @void if (false) null;
        };
    };
    @label end_2;
    {
        __state = -1;
        return;
    };
}


// merging blocks to flatten the code

function fib():Iterator<Int> {
    @label start_1;
    __var_a_1 = 0;
    __var_b_2 = 1;
    @label start_loop_3;
    __cond_3 = true;
    if (!__cond_3) @goto end_loop_4;
    __current = __var_a_1;
    @state next_5;
    return;
    @label next_5;
    @void if (false) null;
    __var_b_2 = __var_a_1 + __var_b_2;
    __current = __var_b_2;
    @state next_6;
    return;
    @label next_6;
    @void if (false) null;
    __var_a_1 = __var_a_1 + __var_b_2;
    @goto start_loop_3;
    @label end_loop_4;
    @void if (false) null;
    @label end_2;
    __state = -1;
    return;
}


// replace label/goto names to integers

function fib():Iterator<Int> {
    @label 0;
    __var_a_1 = 0;
    __var_b_2 = 1;
    @label 1;
    __cond_3 = true;
    if (!__cond_3) {
        __state = 4;
        continue;
    };
    __current = __var_a_1;
    __state = 2;
    return;
    @label 2;
    __var_b_2 = __var_a_1 + __var_b_2;
    __current = __var_b_2;
    __state = 3;
    return;
    @label 3;
    __var_a_1 = __var_a_1 + __var_b_2;
    {
        __state = 1;
        continue;
    };
    @label 4;
    @label 5;
    __state = -1;
    return;
}


// wrapping with a switch

function fib():Iterator<Int> while (true) {
    switch (__state) {
        case -1:{
            throw moon.core.Async.AsyncException.FunctionEnded;
        };
        case 0:{
            __var_a_1 = 0;
            __var_b_2 = 1;
        };
        case 1:{
            __cond_3 = true;
            if (!__cond_3) {
                __state = 4;
                continue;
            };
            __current = __var_a_1;
            __state = 2;
            return;
        };
        case 2:{
            __var_b_2 = __var_a_1 + __var_b_2;
            __current = __var_b_2;
            __state = 3;
            return;
        };
        case 3:{
            __var_a_1 = __var_a_1 + __var_b_2;
            {
                __state = 1;
                continue;
            };
        };
        case 4:{ };
        case 5:{
            __state = -1;
            return;
        };
        default:{
            throw moon.core.Async.AsyncException.InvalidState(__state);
        };
    };
    ++__state;
}


// final pass

function fib():Iterator<Int> {
    var __started:Bool = false;
    var __state:Int = 0;
    var __current:StdTypes.Int = 0;
    var __generator:Iterator<StdTypes.Int> = null;
    var __var_a_1 = null;
    var __var_b_2 = null;
    var __cond_3 = null;
    function __run():Void while (true) {
        switch (__state) {
            case -1:{
                throw moon.core.Async.AsyncException.FunctionEnded;
            };
            case 0:{
                __var_a_1 = 0;
                __var_b_2 = 1;
            };
            case 1:{
                __cond_3 = true;
                if (!__cond_3) {
                    __state = 4;
                    continue;
                };
                __current = __var_a_1;
                __state = 2;
                return;
            };
            case 2:{
                __var_b_2 = __var_a_1 + __var_b_2;
                __current = __var_b_2;
                __state = 3;
                return;
            };
            case 3:{
                __var_a_1 = __var_a_1 + __var_b_2;
                {
                    __state = 1;
                    continue;
                };
            };
            case 4:{ };
            case 5:{
                __state = -1;
                return;
            };
            default:{
                throw moon.core.Async.AsyncException.InvalidState(__state);
            };
        };
        ++__state;
    };
    function __hasNext() {
        return __state >= 0;
    };
    function __next() {
        if (__started) {
            var tmp = __current;
            __run();
            return tmp;
        } else {
            __started = true;
            __run();
            return __next();
        };
    };
    __generator = { hasNext : __hasNext, next : __next };
    return __generator;
}