Generic monad functions with SeqT about fsharpplus HOT 5 CLOSED

That's fine. One more detail: I see you're using a strict monad.plus, by writing monad.plus', but not sure if you read this section of the docs.

There it states:

For layered monads (monad transformers) the general rule is: the monad is strict unless at least one of its constituent types is lazy, in that case the whole monad becomes lazy.

Following. there is a small snippet that helps you when in doubt whether the monad is strict or not.

In your sample, both ReaderT and State are lazy, so even if this version of SeqT is strict (unlike the ideal implementation I mentioned in my previous comment), the whole combination should be a lazy one.

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Actually c) only compiled because I didn't try to consume the results even though intellisense can seemingly detect the types that read_success_c and state_success_c are supposed to be. I'm going to guess this is just a misunderstanding on my end of how to combine Seq and State or that that use case is not supported.

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Going to close this for now until I can make a more concrete repro case / better understand SeqT.

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Just fyi, SeqT and ListT as they are right now don't provide an interesting effect to the inner monad.

A proper SeqT implementation, when combined with Async should derive async sequences, similarly a proper ListT combined with Lazy should automatically derive a lazy list.

I have a ListT on the drafts since almost 2 years, the problem is that due lack of higher kinds, it requires so many type level equations that the compiler slows down a lot, even for trivial cases.

I hope to be able to solve those issues either with a new version of the compiler and/or with v2 of this library with a significant change in the Invoker mechanism.

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Thanks, I am mainly looking for the syntactic sugar to return multiple elements (or ()) which SeqT seems to provide well enough. I was able to solve my problem with SeqT.lift ask and State.get |> ReaderT.lift |> SeqT.lift for ask and get respectively.

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