Trying to install persistent with etlas.

$ etlas install persistent

I get the following error:

src/Language/Haskell/TH/Instances.hs:360:29: error:
Could not deduce (transformers-
arising from a use of ‘MTL.lift’
from the context (Applicative (ReaderT r m),
Monad (ReaderT r m),
Quasi m)
bound by the instance declaration
at src/Language/Haskell/TH/Instances.hs:358:10-39
The type variable ‘t58’ is ambiguous
Note: there are several potential instances:
instance [safe] transformers-
(transformers- e)
-- Defined in ‘transformers-’
instance [safe] Monoid w =>
(RWST r w s)
-- Defined in ‘transformers-’
instance [safe] transformers-
(ReaderT r)
-- Defined in ‘transformers-’ two others
In the expression: MTL.lift
In the expression: MTL.lift $ qReport a b
In an equation for ‘qReport’: qReport a b = MTL.lift $ qReport a b
360 | qReport a b = MTL.lift $ qReport a b
| ^^^^^^^^

Anybody know what this is about?

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For beginners: How do functional languages work?

Very nice talk, highly recommended to get the building blocks of "functional" right.

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Yay, Haskell!
SPJ signing my friends notebook.
And the blue knees on the right: that's me.

What is the exact relationship between Haskell monads and monads in the sense of Category Theory ?

Let C be a concrete category and T a monad on X. Then for any two objects A and B of X we can define a map:

bind_AB: T(A) X Hom(A, TB) -> T(B) (we are Currying)

For let x be in T(A) and f in Hom(A,TB) and m: TT-> T the monad "multiplication".

then we can define bind_AB(x) = m_B(T(f)(x))

recall that m_B is a morphism: T(T(B)) -> T(B)

let ret_A: A -> T(A) be the unit of the monad.

then we can picture the Kleisli category of T and the
composition f o g of
f: A -> T(B) and g: B -> T(C) as being given by

bind_BC(_,g) o f

ret_A is the identity morphism for this composition.

It remains to show that conversely given a Haskell monad we can define a category-theory monad.

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Awesome new role with IOHK for a Community Manager

I'm brand new to Haskell and using an archived EDX course (FP101) with the "Programming in Haskell" book. What I can't seem to find is something like a quick reference to the built-in functions. This would help a lot. I seem to regularly get to a point where I'm sure there's a function available already to do something basic, but I can't find it:(

Any suggies?

Thanx - Charlie

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Hey All,

I am currently working with an awesome blockchain company based in New York who are on the search for talented and experienced Haskell engineers to join the team. Paying up to $180,000 + Benefits + Coins!

Sound like something that could be of interest? Check it out -

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I'm happy to announce a new release of the z3 package, version 4.3, the unofficial Haskell bindings to Microsoft's Z3 API.

Changelog here:

By the way, after many requests I have moved the repository to GitHub:

how to get haskell code execution time (runtime)?
Sorry for my english, I'm brazilian.

I need to know the Real Time, Sys Time and user time (execution) of some codes haskell.

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New release of bv, a Haskell library for bit-vector arithmetic.
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