    {-# LANGUAGE BangPatterns #-}

    -- Ensure that nf' and whnf' are always optimized, even if
    -- criterion-measurement is compiled with -O0 or -fprof-auto (see #184).
    {-# OPTIONS_GHC -O2 -fno-prof-auto #-}
    -- Make the function applications in nf' and whnf' strict (avoiding allocation)
    -- and avoid floating out the computations.
    {-# OPTIONS_GHC -fno-full-laziness #-}

    -- |
    -- Module      : Criterion.Measurement.Types.Internal
    -- Copyright   : (c) 2017 Ryan Scott
    --
    -- License     : BSD-style
    -- Maintainer  : bos@serpentine.com
    -- Stability   : experimental
    -- Portability : GHC
    --
    -- Exports 'fakeEnvironment'.
    module Criterion.Measurement.Types.Internal (fakeEnvironment, nf', whnf') where

    import Data.Int (Int64)

    -- | A dummy environment that is passed to functions that create benchmarks
    -- from environments when no concrete environment is available.
    fakeEnvironment :: env
    fakeEnvironment :: env
    fakeEnvironment = [Char] -> env
    forall a. HasCallStack => [Char] -> a
    error ([Char] -> env) -> [Char] -> env
    forall a b. (a -> b) -> a -> b
    $ [[Char]] -> [Char]
    unlines
      [ "Criterion atttempted to retrieve a non-existent environment!"
      , "\tPerhaps you forgot to use lazy pattern matching in a function which"
      , "\tconstructs benchmarks from an environment?"
      , "\t(see the documentation for `env` for details)"
      ]

    -- Along with Criterion.Types.nfIO' and Criterion.Types.whnfIO', the following
    -- two functions are the core benchmarking loops. They have been carefully
    -- constructed to avoid allocation while also evaluating @f x@.
    --
    -- Because these functions are pure, GHC is particularly smart about optimizing
    -- them. We must turn off @-ffull-laziness@ to prevent the computation from
    -- being floated out of the loop.
    --
    -- For a similar reason, these functions must not be inlined. There are two
    -- possible issues that can arise if they are inlined. First, the work is often
    -- floated out of the loop, which creates a nonsense benchmark. Second, the
    -- benchmark code itself could be changed by the user's optimization level. By
    -- marking them @NOINLINE@, the core benchmark code is always the same.
    --
    -- See #183 and #184 for discussion.

    -- | Generate a function which applies an argument to a function a
    -- given number of times, reducing the result to normal form.
    nf' :: (b -> ()) -> (a -> b) -> a -> (Int64 -> IO ())
    nf' :: (b -> ()) -> (a -> b) -> a -> Int64 -> IO ()
    nf' reduce :: b -> ()
    reduce f :: a -> b
    f x :: a
    x = Int64 -> IO ()
    forall t (m :: * -> *). (Ord t, Num t, Monad m) => t -> m ()
    go
      where
        go :: t -> m ()
    go n :: t
    n | t
    n t -> t -> Bool
    forall a. Ord a => a -> a -> Bool
    <= 0    = () -> m ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
             | Bool
    otherwise = let !y :: b
    y = a -> b
    f a
    x
                           in b -> ()
    reduce b
    y () -> m () -> m ()
    forall a b. a -> b -> b
    `seq` t -> m ()
    go (t
    nt -> t -> t
    forall a. Num a => a -> a -> a
    -1)
    {-# NOINLINE nf' #-}

    -- | Generate a function which applies an argument to a function a
    -- given number of times.
    whnf' :: (a -> b) -> a -> (Int64 -> IO ())
    whnf' :: (a -> b) -> a -> Int64 -> IO ()
    whnf' f :: a -> b
    f x :: a
    x = Int64 -> IO ()
    forall t (m :: * -> *). (Ord t, Num t, Monad m) => t -> m ()
    go
      where
        go :: t -> m ()
    go n :: t
    n | t
    n t -> t -> Bool
    forall a. Ord a => a -> a -> Bool
    <= 0    = () -> m ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
             | Bool
    otherwise = a -> b
    f a
    x b -> m () -> m ()
    forall a b. a -> b -> b
    `seq` t -> m ()
    go (t
    nt -> t -> t
    forall a. Num a => a -> a -> a
    -1)
    {-# NOINLINE whnf' #-}