[Haskell-cafe] Commutative monads vs Applicative functors
lemming at henning-thielemann.de
Sun May 18 09:06:59 EDT 2008
On Wed, 14 May 2008, David Menendez wrote:
> On Tue, May 13, 2008 at 9:06 PM, Ronald Guida <oddron at gmail.com> wrote:
>> I have a few questions about commutative monads and applicative functors.
>> >From what I have read about applicative functors, they are weaker than
>> monads because with a monad, I can use the results of a computation to
>> select between alternative future computations and their side effects,
>> whereas with an applicative functor, I can only select between the
>> results of computations, while the structure of those computations and
>> their side effects are fixed in advance.
>> But then there are commutative monads. I'm not exactly sure what a
>> commutative monad is, but my understanding is that in a commutative
>> monad the order of side effects does not matter.
>> This leads me to wonder, are commutative monads still stronger than
>> applicative functors, or are they equivalent?
>> And by the way, what exactly is a commutative monad?
Interestingly I used a Writer monad with a commutative monoid recently,
which is also an example of a commutative monad.
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