Simon Peyton Jones

I'm not sure it'll be very fruitful for us.

We'd have to get a lot more details of the type system sorted out to know what to say.

But at this very high level overview, the big point I'm trying to make is weak type systems

Get in the way.

Type systems are meant to reject programs that will go wrong.

But my function that reverses a list of integers, it will also reverse the list of characters.

So it's tiresome to be told, no, that is a bad program.

I want to be able to write that it has to have four A list of A to list of A.

So the idea of making the type system more complicated is to say, programs that you want to run, you can still write in your static type system.

Now, you might say, well, blimey, if that's all, why don't we just get rid of the static type system altogether?

Now we could run all of those programs.

But the trouble is you can run too many programs now.

You can run programs that will crash at runtime.

And that's very, very, very bad.

And we all know the costs of programs that crash in deployment.

that you could have crashed before you even started to run them, before you even ran your first test, right?

Before you even linked it into an executable, that's really good.

But the biggest benefit of a static type system, in my humble opinion, is maintainability.

If you have a program written in, I don't know, Perl or Ruby,

or Lisp in its basic form, and it was written 15 years ago, and the original author has left, and all of the people who were involved at the time it was written have left, then that program is very difficult to maintain.