A lenses library for Haskell.
An extensive library which provides families of lenses, isomorphisms, folds, traversals, getters and setters.
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Questions tagged [haskell-lens]
454 questions
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Failed to install lens-4.2 : Cabal 1.20.0.2, GHC 7.6.3, Ubuntu 14.04
I was installing leksah ( "cabal install leksah" ) & the it failed with a message similar to below one ( about lens 4.2 dependency )
I tried installing the lasted version instead but that didn't solved my problem . ( I have unregistered that -…
AmirHossein
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Tracing out the type of partial application of functions
I have been inspecting the type of Lens to understand it and have trouble figuring out the resulting type of partial application there.
Initial type is like this: type RefF a b = forall f. Functor f => (b -> f b) -> (a -> f a)
The above type applied…
Sibi
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1 answer
Traversing and adding elements to a Data.Tree using Lenses in Haskell
I'm starting to use lenses and until now I've been unable to use them in a concrete part of a codebase I'm writing. My objective is to update a rose tree structure such as the one in Data.Tree by adding a new node inside one of the existing ones. To…
Jesuspc
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In the lets-lens tutorial, how do you refactor out the call to traverse in order to implement over?
In the exercises I have implemented fmapT:
-- Let's remind ourselves of Traversable, noting Foldable and Functor.
--
-- class (Foldable t, Functor t) => Traversable t where
-- traverse ::
-- Applicative f =>
-- (a -> f b)
-- -> t a
--…
rcmerci
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