For me there were two important "aha" moments. Right at the beginning I was drawn in by using ADTs and pattern-matching on them. It's so simple and plain and now it's the first thing I miss in any other language I have to work with. I feel like this would make a short, compelling example for programmers coming from any other background.

The second was reading Wadler's "Monads for Functional Progamming" (and reading it a second and third time, if we're being honest). The ways in which he takes three seemingly disconnected examples and reduces them to this broader mathematical abstraction: I found it quite beautiful and surprising once I fully appreciated it.


On Wed, Jul 11, 2018 at 7:29 AM Ionuț G. Stan <ionut.g.stan@gmail.com> wrote:
This is not necessarily related to Haskell, as I've had this A-HA moment
while watching the 1984 SIPC lectures from MIT.

Anyway, at some point, Mr Sussman (or was it Mr Abelson?) used `+` as an
argument to another function. I was bedazzled!

First of all, it was the syntactic novelty — `+` was not some rigid part
of the syntax, it was just a name — secondly, it was not any name, it
was the name of a *function*  that was sent to another function. It was
probably my first encounter with higher-order functions.

If I remember correctly, the code was along the lines of:

foldl (+) 0 [1,2,3]


On 11/07/2018 15:10, Simon Peyton Jones via Haskell-Cafe 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
>
>
>
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--
Ionuț G. Stan  |  http://igstan.ro  |  http://bucharestfp.ro
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Erik Aker