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

[PY]

13.07.2018 02:40, Tony Morris wrote:
> On python, we are fixing it (WIP):
> https://github.com/qfpl/hpython
>
> Did you see the recent "default mutable arguments" post?
> https://lethain.com/digg-v4/
>
> Here is a Haskell program that transforms any python program that uses
> default mutable arguments:
> https://github.com/qfpl/hpython/blob/master/example/FixMutableDefaultArguments.hs
>
> Someone once said that python will never have tail call optimisation.
> Here is the Haskell program that transforms any Python (direct only)
> tail call into a loop:
> https://github.com/qfpl/hpython/blob/master/example/OptimizeTailRecursion.hs
>
> Two python programmers once argued over preferred indentation levels.
> Let's put their disagreement into a Haskell function so that they can
> stop arguing:
> https://github.com/qfpl/hpython/blob/master/example/Indentation.hs

IMHO will be good to port such successful "experiments" to PyPy project 
in some way, if it's possible

>
> On 07/12/2018 07:58 PM, Brett Gilio wrote:
>> Python is poison, indeed. ;)
>>
>> Brett Gilio
>> brettg at posteo.net | bmg at member.fsf.org
>> Free Software -- Free Society!
>>
>> On 07/12/2018 04:56 AM, Graham Klyne wrote:
>>> Although I don't program regularly in Haskell these days (my poison
>>> is Python, mainly for Web framework support), I do occasionally find
>>> myself coding tricky manipulations in Haskell first as I find it
>>> easier to concentrate on the essentials of an algorithm.  Once I have
>>> the Haskell code written and tested, I generally find it fairly easy
>>> to map the algorithm into Python (using higher order functions as
>>> appropriate).
>>>
>>> Here are some examples:
>>>
>>> https://github.com/gklyne/annalist/blob/master/spike/rearrange-list/move_up.lhs
>>>
>>> https://github.com/gklyne/annalist/blob/master/spike/tree-scan/tree_scan.lhs
>>>
>>>
>>> And the corresponding code in the actual application:
>>>
>>> https://github.com/gklyne/annalist/blob/4d21250a3457c72d4f6525e5a4fac40d4c0ca1c8/src/annalist_root/annalist/views/entityedit.py#L2489
>>>
>>>
>>> https://github.com/gklyne/annalist/blob/master/src/annalist_root/annalist/models/entity.py#L245
>>>
>>>
>>> #g
>>> -- 
>>>
>>>
>>> On 11/07/2018 13:10, 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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>
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