quickcheck-dynamic-3.0.0: src/Test/QuickCheck/DynamicLogic/SmartShrinking.hs

module Test.QuickCheck.DynamicLogic.SmartShrinking (shrinkSmart) where

import Test.QuickCheck

-- | This combinator captures the 'smart shrinking' implemented for the
-- Smart type wrapper in Test.QuickCheck.Modifiers.
shrinkSmart :: (a -> [a]) -> Smart a -> [Smart a]
shrinkSmart shr (Smart i x) = take i' ys `ilv` drop i' ys
  where
    ys = [Smart j y | (j, y) <- [0 ..] `zip` shr x]
    i' = 0 `max` (i - 2)
    [] `ilv` bs = bs
    as `ilv` [] = as
    (a : as) `ilv` (b : bs) = a : b : (as `ilv` bs)