[Haskell-cafe] On finding the right exposition... (Monads)

Viktor Dukhovni ietf-dane at dukhovni.org
Fri Sep 17 20:50:25 UTC 2021

On Fri, Sep 17, 2021 at 10:29:41PM +0200, Joachim Durchholz wrote:

> > Unsurpsingly, I have a mental model built around sequencing of internal
> > state updates while passing data from one state to use in choosing the
> > next state transition.
> I have been finding the Monad expositions misleading - that idea that 
> monads are for sequencing or transitions or mutable state always felt 
> wrong to me, since the monad laws don't talk about any of these things 
> at all.

That's the nature of mental models, they're first approximations with
possible refinements.  Yes, there are monads for which State is a poor
analogy.  The `Cont` monad comes to mind, one needs to "think different"
when reasoning about `callCC`, `shift` and `reset`

`State` as a mental model for monads captures basic sequencing with
possible internal "effects" well enough to be a reasonable first
approximation.  Already with List exploring all possible paths the
fit is not ideal.


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