[Haskell-cafe] Better writing about Haskell through multi-metaphor learning

[David Feuer]

Best of all is to avoid being too wrong in your teaching. No, don't teach
children radians, but don't teach them degrees either (except on the side).
Teach them *turns*, and later explain that a degree is 1/360th of a turn,
and still later that a radian is 1/(2π) turns.

On Sun, Sep 19, 2021, 5:07 PM Richard Eisenberg <lists at richarde.dev> wrote:

> Other understandings of informal terms will differ, but here is how I see
> it:
>
> * "Workflow" applies equally well to Monad as to Arrow. Both capture the
> idea of information flowing from one computation to the next.
>
> * "Programmable semicolon" seems a better fit for Monad than for Arrow. In
> C, I can say:
>
> > int result = do_some_thing();
> > if (result > 10)
> >   big_result();
> > else
> >   small_result();
>
> That is, the future flow of my computation can depend on an earlier
> result. This is possible with Monad but not with Arrow. So, if I had
> thought that Arrow was a programmable semicolon, I would have felt
> short-changed a bit when actually learning what Arrow was.
>
> Popping up a level: for me, the value in these ideas is not their
> precision, but rather their familiarity. Give me intuition first,
> correctness later.
>
> Sidenote (please feel free to skip!): In later secondary school and
> throughout university, I kept learning things that refined earlier
> knowledge -- indeed suggesting that earlier knowledge was wrong. For
> example, radians are *much* more convenient to work with than degrees,
> which are kind of ridiculous. I resolved then that I would teach my kids
> how to measure angles in radians from the start: why bother with the
> inferior unit? Now I have a daughter, who is learning degrees. Why? Because
> degrees are simpler to start with: we can describe a circle or a right
> angle without any irrational numbers! So, we build intuition with degrees,
> and then she'll switch to radians when the time comes. Another example: we
> now know that object do not accelerate parabolically under the influence of
> gravity, because of general relativity. But general relativity is hard, so
> we still teach about parabolic curves for objects in freefall. Once a
> student knows more physics, they can return and refine their knowledge.
>
> So can it be with Haskell. We sometimes get so caught up in being "right"
> and precise, that we forget that it is sometimes useful to paper over some
> details for the sake of intuition. This means we sometimes have to say
> "wrong" things. (For example, I have said that "IO Int" is just an Int
> tagged with a flag that says the function can do I/O and must be written
> with do-notation.) But if the goal is learning, sometimes the "wrong" thing
> is the right thing.
>
> Richard
>
> > On Sep 18, 2021, at 4:00 AM, Tom Ellis <
> tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk> wrote:
> >
> > On Sat, Sep 18, 2021 at 11:56:37AM +0900, Michael Turner wrote:
> >> Workflow is a metaphor at one useful level. "Programmable semicolon"
> >> is a metaphor at another useful level.
> > [...]
> >> "Workflow" helped me. And now "programmable semicolon" is helping a
> >> little, in another way.
> >
> > What troubles me about "workflow" and "programmable semicolon" is the
> > question of whether they also apply to Arrow[1].
> >
> > * If they do, then in what sense can "workflow" and "programmable
> >  semicolon" said to help with understanding of *Monad*?
> >
> > * If they don't, then why not?  I don't see it.
> >
> > One possible answer is that they do, but those descriptions are only
> > intended to improve understanding about purpose not about technical
> > details (I think this is what Michael is suggesting).
> >
> > Tom
> >
> >
> >
> > [1]
> https://www.stackage.org/haddock/lts-17.7/base-4.14.1.0/Control-Arrow.html
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