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modifyingTraverse #115

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12 changes: 12 additions & 0 deletions src/Data/Lens/Traversal.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,11 +26,13 @@ module Data.Lens.Traversal
, elementsOf
, itraverseOf
, cloneTraversal
, (%%=), modifyingTraverse
, module ExportTypes
) where

import Prelude

import Control.Monad.State.Class (class MonadState, get, put)
import Control.Alternative (class Alternative)
import Control.Plus (empty)
import Data.Lens.Indexed (iwander, positions, unIndex)
Expand Down Expand Up @@ -146,3 +148,13 @@ iforOf = flip <<< itraverseOf

cloneTraversal :: forall s t a b. ATraversal s t a b -> Traversal s t a b
cloneTraversal l = wander (runBazaar (l (Bazaar identity)))

-- | Modify the foci of a `Setter` in a monadic state with a traversal.
modifyingTraverse
:: forall s a b m
. MonadState s m
=> Traversal s s a b
-> (a -> m b)
-> m Unit
modifyingTraverse t f = get >>= traverseOf t f >>= put
infix 4 modifyingTraverse as %%=