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

[Francesco Ariis]

On Wed, Jul 11, 2018 at 12:10:21PM +0000, Simon Peyton Jones via Haskell-Cafe wrote:
> 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.

If your most of your audience uses a dynamically typed language,
I would introduce type inference and how small, painful bugs can
be tracked down by the compiler without having to write a single
type signature bar top level.

Another good one is implementing a tricky function with holes
(in what I have seen described as `hole-driven` development.

Unfortunately, one of Haskell strongest suit (ease of refactoring)
doesn't really shine in bite-sized examples!