Re: [Haskell-cafe] What is your favourite Haskell "aha" moment?

Op 12 jul. 2018, om 15:01 heeft Brett Gilio het volgende geschreven:

Alexey, could you expand on what you mean in your first point? I am quite intrigued. I do not use Haskell often, but that could be something of interest to me in-and-out of Haskell.

In the old days, when I wrote Pascal programs, and I wanted to swap values I wrote code like: function swap (var x, y: integer); begin x := x+y; y := x - y; x := x - y end; Only to find out that if I wanted a swap for a different type this does not work. Hence a lot of coding, and hardly re-use and very error prone. How many functions can’t you write that have this type. So the question is how many functions can you write with the type (a, a) -> (a, a). If you randomly generate functions of this type there is a chance of 25% you get the right one. But things become even better: swap (a, b) = (b, a) Once you ask for the type you get (a, b) -> (b, a), hence the type completely specifies what swap computes, and the function is even more general than the version of the type above. Doaitse

Brett Gilio brettg@posteo.net | bmg@member.fsf.org Free Software -- Free Society!

On 07/12/2018 07:46 AM, Alexey Raga wrote:

...

Not sure if it counts as "aha moments", but when I started with Haskell I had two major reasons (not in any importance order): 1. The ability to define the specification (types) and then "just" follow them in implementation. Sometimes even without having a clear understanding of the things I was using, I felt (and still feel) guided towards the right solution. 2. The ability to refactor fearlessly is a _massive_ productivity boost. Hard to underestimate. Regards, Alexey. On Wed, Jul 11, 2018 at 10:10 PM Simon Peyton Jones via Haskell-Cafe mailto:haskell-cafe@haskell.org> wrote: Friends____ In a few weeks I’m giving a talk to a bunch of genomics folk at the Sanger Institute https://www.sanger.ac.uk/ about Haskell. They do lots of programming, but they aren’t computer scientists.____ I can tell them plenty about Haskell, but I’m ill-equipped to answer the main question in their minds: /why should I even care about Haskell/? I’m too much of a biased witness. ____ So I thought I’d ask you for help. War stories perhaps – how using Haskell worked (or didn’t) for you. But rather than talk generalities, I’d love to illustrate with copious examples of beautiful code. ____ * Can you identify a few lines of Haskell that best characterise what you think makes Haskell distinctively worth caring about? Something that gave you an “aha” moment, or that feeling of joy when you truly make sense of something for the first time.____ The challenge is, of course, that this audience will know no Haskell, so muttering about Cartesian Closed Categories isn’t going to do it for them. I need examples that I can present in 5 minutes, without needing a long setup.____ To take a very basic example, consider Quicksort using list comprehensions, compared with its equivalent in C. It’s so short, so obviously right, whereas doing the right thing with in-place update in C notoriously prone to fencepost errors etc. But it also makes much less good use of memory, and is likely to run slower. I think I can do that in 5 minutes.____ Another thing that I think comes over easily is the ability to abstract: generalising sum and product to fold by abstracting out a functional argument; generalising at the type level by polymorphism, including polymorphism over higher-kinded type constructors. Maybe 8 minutes.____ But you will have more and better ideas, and (crucially) ideas that are more credibly grounded in the day to day reality of writing programs that get work done.____ Pointers to your favourite blog posts would be another avenue. (I love the Haskell Weekly News.)____ Finally, I know that some of you use Haskell specifically for genomics work, and maybe some of your insights would be particularly relevant for the Sanger audience.____ Thank you! Perhaps your responses on this thread (if any) may be helpful to more than just me.____ Simon____ _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post. _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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