The A-Z of Programming Languages: Haskell

Simon Peyton-Jones tells us why he is most proud of Haskell's purity, type system and monads.

Simon Peyton-Jones

Simon Peyton-Jones

Speaking of the evolution of Haskell, what do you think of variants such as Parallel, Eager and Distributed Haskell, and even Concurrent Clean?

This is all good stuff. This is what Haskell is for. Haskell specifically encourages diversity. By calling Haskell ’98 that name instead of ‘Haskell’, we leave the Haskell brand name free to be applied to lots of things. Anything that has Haskell in the name is usually pretty close; it’s usually an extension of Haskell ’98. I don’t know anything that’s called *something* Haskell and that doesn’t include Haskell ’98 at least.

These aren’t just random languages that happen to be branded, like JavaScript which has nothing to do with Java. They [JavaScript] just piggy-backed on the name. They thought if it was Java, it must be good!

Do you find yourself using any of these languages?

Yes. Concurrent Haskell is implemented in GHC, so if you say I’m using Concurrent Haskell you’re more or less saying you’re using GHC with the concurrency extension Data Parallel. Haskell is also being implemented in GHC, so many of these things are actually all implemented in the same compiler, and are all simultaneously usable. They’re not distinct implementations.

Distributed Haskell is a fork of GHC. Some older versions run on multiple computers connected only to the Internet. It started life as being only part of GHC, but you can’t use it at the same time as the concurrency extensions, or a lot of the new things that are new in GHC, because Distributed Haskell is a “fork”. It started life as the same code base but it has diverged since then. You can’t take all of the changes that have been made in GHC and apply them to the distributed branch of the fork – that wouldn’t work.

Concurrrent Clean on the other hand is completely different. It’s a completely different language; it’s got a completely different implementation. It existed before Haskell did and there’s a whole different team responsible, led by Rinus Plasmeijer. At one stage I hoped that we would be able to unify Haskell and Clean, but that didn’t happen. Clean’s a very interesting and good language. There’s lots of interesting stuff in there.

When did you think that the two might combine?

When we first started, most of us [the Haskell committee] had small prototype languages in which we hadn’t yet invested very much, so we were happy to give them all up to create one language. I think Rinus had more invested in Concurrent Clean, however, and so chose not to [participate in Haskell]. I have no qualms with that, as diversity is good and we don’t want a mono-culture, as then you don’t learn as much.

Clean has one completely distinct feature which is not in Haskell at all, which is called uniqueness typing. This is something that would have been quite difficult to merge into Haskell. So there was a good reason for keeping two languages… It’s another thing like modules that would have been a big change. We would have had a lot of ramifications and it’s not clear that it would have been possible to persuade all of the Haskell participants that the ramifications were worth paying for. It’s the do one thing well, again.

That sounds like the language’s aim: do one thing and do it well…

Yes. That’s right.

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