Type checks and casts

fun takeOptInt(v: int?) {}

fun main() {
    takeOptInt(100);    // ok, `int` to `int?`
    takeOptInt(null);   // ok, `null` to `int?`
}

fun demo() {
    var number: int32 = 100;   // auto cast `int` to `int32`
}

fun main() {
    var number: int = true;
}

file.tolk:2:23: error: can not assign `bool` to variable of type `int`
           hint: use `as` operator for UNSAFE casting: `<some_expr> as int`

    // in function `main`
   2 |     var number: int = true;
     |                       ^^^^

var number: int = true as int;    // -1

fun doSmth(c: cell) {}

fun analyzeStorage(nCells: int, lastCell: cell?) {
    if (nCells) {           // then lastCell 100% not null
        doSmth(lastCell!);  // use ! for this fact
    }
}

if (lastCell != null) {
    // here lastCell is `cell`, not `cell?`
}

fun demo(v: int | Point | cell) {
    if (v is Point) {
        return v.x + v.y;
    }
    // v is `int | cell` here
}