On: John Carmack: Script Interpreters Considered Harmful

[jrockway]

Why? Python already requires type annotations. For example, if you have a string "42", you can't just add 1 to it to get the number 43, you have to say int("42") + 1 or it will throw a type error.

[joesb → jrockway]

It throws type error at run time, not compile time.

To be a statically type language you would need to throw the error at compile time.

How do you raise (or not raise) error of this code at compile time and still make it feel like dynamic type language?

    x = (rand() > 0.5) ? 42 : "42"
    y = x + 1;

[jrockway → joesb]

The type of x is Int|String

The type of (+ 1) is Int -> Int

The type of y is Int

Because x is of type Int|String and it's passed to a function that can only operate on Int, the program fails to compile.

[kingkilr → jrockway]

I highly reccomend you read, "Localized type inference of atomic types in python" by Brett Cannon (2005), it shines a light on just how much this doesn't work.

[ned_batchelder → jrockway]

So when you said, "looks just like Python," you literally meant, "lexically looks like Python," because you aren't building a language that works just like Python.

[DasIch → jrockway]

That is not a type annotation. Python is simply strongly typed that has nothing to do with whether or not the language is dynamically or statically typed.