Simon Peyton Jones

Give them what they say they want.

If we build it, they will come kind of deal.

Avoid success at all costs.

Or if you parenthesize it the other way, it says avoid success at all costs.

At all costs, avoid success.

And that's saying, that's a little joke, but it says, if you're too successful and have too many users, it becomes more difficult to make changes.

And we experience that right now.

So I devote many, many more of my personal cycles to backward compatibility issues than ever I did.

I have devoted hundreds of hours, hours and hours, well, days and days, weeks and weeks in the last year or two to the following, what seems to be a very simple property.

If you can compile a program, a package in a whole program with GHC 10.0 and we released GHC 10.2, you should be able to compile that same package unchanged with GHC 10.2.

Seems reasonable, right?

After all, 10.2 should just be better.

But no, JTC has never had that property.

And making it have that property has turned out to be very, very time consuming.

Previously, we just never cared.

Then we started to care, but thought it was a lot of work.

And now we're investing the work.

I think it may be the best thing that's happened to statically typed languages for a long time because, as we've been discussing,

With a static type system, you cut down the space of programs that the LLM can generate.

Because it is perfectly capable of running the compiler and saying, oh, darn, that was a bad program, better fix it.