通过镜头折叠或连接Aeson阵列 [英] Folding or concatMap-ing an Aeson Array via lenses

问题描述

我从

I've been starting at https://www.stackage.org/haddock/lts-12.1/lens-aeson-1.0.2/Data-Aeson-Lens.html and https://www.stackage.org/haddock/lts-12.1/lens-4.16.1/Control-Lens-Fold.html trying to figure out how to write an expression that allows me to construct something of the following type:

import Data.Aeson as A

functionIWant 
  :: (Vector A.Value)
  -> (A.Value -> [a])
  -> [a]

推荐答案

有两种镜头功能可用于将与常规 Foldable 相关的功能提升"到镜头世界:

There are two lens functions that are used to "lift" regular Foldable-related functions to the lensy world:

• folded 折叠在 Foldable 容器的所有元素上，在这种情况下，它将是 Vector .
• folding 会提升一个返回 Foldable 结果的函数.

• folded that folds over all the elements of a Foldable container, in this case it would be the Vector.
• folding that lifts a function that returns a Foldable result.

您可以将它们组合成新的 Fold ，然后使用

You can compose them into a new Fold and then use toListOf to obtain the final list.

对于 Traversable ，还有一个 folded 的类似物，称为

There is also an analogue of folded for Traversable, called traversed.

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