[Haskell-cafe] free vs. operational vs. free-operational

Alejandro Serrano Mena trupill at gmail.com
Wed Nov 27 07:49:13 UTC 2013

Thanks for the pointer! :)
The extensible-effects package seems very interesting. I would really like
to have instances of all usual monads: Reader, Writer, State.Lazy and so on
in the package. Maybe that's a project for the future :)

Even so, I'm still interesting in understanding my original concerns with
free vs. operational, specially the "baking algebraic laws" part and
whether it's good to replace operational with free-operational altogether.

2013/11/26 <oleg at okmij.org>

> Alejandro Serrano Mena wrote:
> > I really like the separation between providing a data type and then a
> > interpretation that operational embodies...
> Then perhaps you may like extensible effects then. They are designed
> around the separation of requestors and their interpreters. However, the
> set of requests is open (and can be extended at any time without
> recompiling the program). Likewise the interpreters can be extended
> incrementally. One can add an interpreter for an effect without caring
> what other effects are there -- unless one has some reason for caring
> about other effects (e.g.,m for finalization). One may then snoop on
> other effects while interpreting. Moreover, the handlers may be
> scattered around program; they don't have to be all at the very top.
> Crucially, unlike data types a la carte, extensible effects provide
> effect encapsulation: one can not only add effects but subtract them,
> by completely handling the effects. The type system ensures that all
> effects must be completely handled at the end.
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