Re: [Haskell-cafe] MTL vs Free-monads, what are your experiences

On Fri, Oct 14, 2016 at 6:00 PM, Matt wrote:

The mtl technique subsumes the free monad technique. if you have a term:

getCurrentTime :: MonadClock m => m UTCTime

Then you can *use* that function as anything that satisfies the constraint. Given an `IO` instance, that can just get the current time: `getCurrentTime :: IO UTCTime`. Given a mock instance, that can be `getCurrentTime :: MockClock UTCTime`. Given an instance on Free, you'd have `getCurrentTime :: Free CurrentTimeF UTCTime`

Thanks Matt. I think that was a nice explanation. Right now I'm focusing on the composition and natural transformations of free-monads, but I still haven't checked the MTL approach.

I generally find it more pleasant to write functions in mtl style. If you're after more concrete guarantees on the DSL you're building and see yourself doing a lot of introspection and optimization, then a Free monad approach fits the bill.

I definitely like monad transformers. But I guess I'd have to explain the specific case in another thread.

Matt Parsons

On Fri, Oct 14, 2016 at 11:35 AM, Damian Nadales wrote:

...

Hi,

I was looking into free monads for designing a DSL for describing scenarios of the form: scenario = do aId <- createA b0Id <- createB id b1Id <- createB id link b0 b1

In our company we use a graph database, and currently we're setting up the test data using raw queries O.O So I wanted to come up with a better abstraction, and also enable us to do property based testing (by testing on random scenarios like the one above).

Anyway, I ran into this presentation: http://www.slideshare.net/jdegoes/mtl-versus-free http://degoes.net/articles/modern-fp-part-2

In which monad transformers and free monads are compared. Do you have any experience using any of these approaches. If so would you mind sharing? ;)

Thanks! Damian _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.