<div dir="ltr">Some code examples that I usually show/explain to someone who is interested in Haskell but have no previous exposure:<div><br></div><div>ADTs. Even for something as simple as</div><div><br></div><div>data ShoppingCartCommand</div><div> = CreateCart UserId</div><div> | AddToCart CartId ProductId Quantity</div><div> | ClearCart CartId</div><div> deriving (Eq, Show)</div><div><br></div><div>This would be many-many lines of non-trivial C# or Java code (you would need to think about abstract classes or interfaces, correctly override toString, equality and getHashCode, write tests for all this, etc). </div><div><br></div><div>If the audience is familiar with C#, then explaining the ability to abstract over type constructors may work well. In C# there is no way to generalise over, say, IEnumerable<T> and IObservable<T>. If you want to accept both then you'd have to write the same LINQ statements twice (or convert one into another, which is not always possible).</div><div><br></div><div>Regards,</div><div>Alexey.</div><div><br></div><div><br></div><div><div class="gmail_quote"><div dir="ltr">On Wed, Jul 11, 2018 at 10:10 PM Simon Peyton Jones via Haskell-Cafe <<a href="mailto:haskell-cafe@haskell.org">haskell-cafe@haskell.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Friends<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">In a few weeks I’m giving a talk to a bunch of genomics folk at the
<a href="https://www.sanger.ac.uk/" target="_blank">Sanger Institute</a> about Haskell. They do lots of programming, but they aren’t computer scientists.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">I can tell them plenty about Haskell, but I’m ill-equipped to answer the main question in their minds:
<i>why should I even care about Haskell</i>? I’m too much of a biased witness.<br>
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<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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. <u></u><u></u></span></p>
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<li class="m_-4821601820748067223MsoListParagraph" style="margin-left:0cm"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></li></ul>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Pointers to your favourite blog posts would be another avenue. (I love the Haskell Weekly News.)<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">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.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Thank you! Perhaps your responses on this thread (if any) may be helpful to more than just me.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Simon<u></u><u></u></span></p>
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