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

So what are you proudest of in terms of the languages development and use?

I think you can probably guess by now! Sticking to purity, the invention of monads and type classes. We haven’t even talked about type classes yet. I think Haskell’s types system, which started with an innovation called type classes, has proved extremely influential and successful. It’s one distinctive achievement that was in Haskell since the very beginning. But even since then, Haskell has proved to be an excellent type system laboratory. Haskell has lots of type system features that no other language has. I’m still working on further development of this, and I’m pretty proud about that.

And where do you think computer languages will be heading in the next 5 – 20 years or so? Can you see any big trends etc?

It’s back to effects. I don’t know where programming in general will go, but I think that over the next 10 years, at that sort of timescale, we’ll see mainstream programming becoming much more careful about effect – or side effects. That’s my sole language trend that I’ll forecast. And of course, even that’s a guess, I’m crystal ball gazing.

It’s no good just reading a book, you’ve got to write a purely functional program.

Specifically, I think languages will grow pure or pure-ish subsets. There will be chunks of the language, even in the main imperative languages, that will be chunks that are pure.

Given all of your experience, what advice do you have for students or up and coming programmers?

Learn a wide range of programming languages, and in particular learn a functional language. Make sure that your education includes not just reading a book, but actually writing some functional programs, as it changes the way you think about the whole enterprise of programming. It’s like if you can ski but you’ve never snowboarded: you hop on a snowboard and you fall off immediately. You initially think humans can’t do this, but once you learn to snowboard it’s a different way of doing the same thing. It’s the same with programming languages, and that radically shifted perspective will make you a better programmer, no matter what style of programming you spend most of your time doing. It’s no good just reading a book, you’ve got to write a purely functional program. It’s not good reading a book about snow boarding – you have to do it and fall off a lot before you train your body to understand what’s going on.

Thanks for taking the time to chat to me today. Is there anything else you’d like to add?

I’ll add one other thing. Another distinctive feature of Haskell is that it has a very nice community. We haven’t talked about the community at all, but Haskell has an extremely friendly sort of ecosystem growing up around it. There’s a mailing list that people are extremely helpful on, it has a wiki that is maintained by the community and it has an IRC channel that hundreds of people are on being helpful. People often comment that it seems to be an unusually friendly place, compared to experiences they’ve had elsewhere (and I can’t be specific about this as I genuinely don’t know.) I don’t know how to attribute this, but I’m very pleased that the Haskell community has this reputation as being a friendly and welcoming place that’s helpful too. It’s an unusually healthy community and I really like that.

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