Lens.hs

-----------------------------------------------------------------------------
-- |
-- Module      :  Control.Parallel.Strategies.Lens
-- Copyright   :  (C) 2012 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  provisional
-- Portability :  portable
--
-- A 'Lens' or 'Traversal' can be used to take the role of 'Traversable' in
-- @Control.Parallel.Strategies@, enabling those combinators to work with
-- monomorphic containers.
----------------------------------------------------------------------------
module Control.Parallel.Strategies.Lens
  ( evalOf
  , parOf
  , after
  , meanwhile
  ) where

import Control.Lens
import Control.Parallel.Strategies

-- | Evaluate the targets of a 'Lens' or 'Traversal' into a data structure
-- according to the given strategy.
--
-- > evalTraversable = evalTraversal traverse
--
-- > evalTraversal = id
--
-- > evalTraversal :: Simple Lens a b -> Strategy b -> Strategy a
-- > evalTraversal :: Simple Traversal a b -> Strategy b -> Strategy a
--
-- > evalTraversal :: (b -> Eval b) -> a -> Eval a) -> Strategy b -> Strategy a
evalOf :: LensLike Eval a a b b -> Strategy b -> Strategy a
evalOf l = l

-- | Evaluate the targets of a 'Lens' or 'Traversal' according into a
-- data structure according to a given 'Strategy' in parallel.
--
-- > parTraversable = parTraversal traverse
--
-- > parTraversal :: Simple Lens a b -> Strategy b -> Strategy a
-- > parTraversal :: Simple Traversal a b -> Strategy b -> Strategy a
--
-- > parTraversal :: ((b -> Eval b) -> a -> Eval a) -> Strategy b -> Strategy a
parOf :: LensLike Eval a a b b -> Strategy b -> Strategy a
parOf l s = l (rparWith s)

-- | Transform a 'Lens', 'Fold', 'Getter', 'Setter' or 'Traversal' to
-- first evaluates its argument according to a given strategy, before proceeding.
--
-- > after rdeepseq traverse
after :: Strategy a -> LensLike f a b c d -> LensLike f a b c d
after s l f = l f $| s

-- | Transform a 'Lens', 'Fold', 'Getter', 'Setter' or 'Traversal' to
-- evaluate its argument according to a given strategy in parallel with evaluating.
--
-- > meanwhile rdeepseq traverse
meanwhile :: Strategy a -> LensLike f a b c d -> LensLike f a b c d
meanwhile s l f = l f $|| s