Add an nfIO function.

--HG--
extra : convert_revision : 88459844b44422256ae6f934cb0a50a0ff0bbbc8

Criterion.hs

@@ -15,6 +15,7 @@ module Criterion
     , Benchmark
     , Pure
     , nf
+    , nfIO
     , whnf
     , bench
     , bgroup
@@ -33,7 +34,7 @@ import Criterion.Measurement (getTime, runForAtLeast, secs, time_)
 import Criterion.Monad (Criterion, getConfig, getConfigItem)
 import Criterion.Plot (plotWith, plotKDE, plotTiming)
 import Criterion.Types (Benchmarkable(..), Benchmark(..), Pure,
-                        bench, bgroup, nf, whnf)
+                        bench, bgroup, nf, nfIO, whnf)
 import Data.Array.Vector ((:*:)(..), concatU, lengthU, mapU)
 import Statistics.Function (createIO, minMax)
 import Statistics.KernelDensity (epanechnikovPDF)

Criterion/Main.hs

@@ -32,6 +32,7 @@ module Criterion.Main
     , bench
     , bgroup
     , nf
+    , nfIO
     , whnf
     -- * Running benchmarks
     , defaultMain
@@ -50,7 +51,7 @@ import Criterion.IO (note, printError)
 import Criterion.MultiMap (singleton)
 import Criterion.Monad (Criterion, withConfig)
 import Criterion.Types (Benchmarkable(..), Benchmark(..), Pure, bench,
-                        benchNames, bgroup, nf, whnf)
+                        benchNames, bgroup, nf, nfIO, whnf)
 import Data.List (isPrefixOf, sort)
 import Data.Monoid (Monoid(..), Last(..))
 import System.Console.GetOpt

Criterion/Types.hs

@@ -31,6 +31,7 @@ module Criterion.Types
     , Pure
     , whnf
     , nf
+    , nfIO
     , bench
     , bgroup
     , benchNames
@@ -52,14 +53,25 @@ data Pure where
     WHNF :: (a -> b) -> a -> Pure
     NF :: NFData b => (a -> b) -> a -> Pure
 
+-- | Apply an argument to a function, and evaluate the result to weak
+-- head normal form (WHNF).
 whnf :: (a -> b) -> a -> Pure
 whnf = WHNF
 {-# INLINE whnf #-}
 
+-- | Apply an argument to a function, and evaluate the result to head
+-- normal form (NF).
 nf :: NFData b => (a -> b) -> a -> Pure
 nf = NF
 {-# INLINE nf #-}
 
+-- | Perform an action, then evaluate its result to head normal form.
+-- This is particularly useful for forcing a lazy IO action to be
+-- completely performed.
+nfIO :: NFData a => IO a -> IO ()
+nfIO a = a >>= \k -> return $! rnf k
+{-# INLINE nfIO #-}
+
 instance Benchmarkable Pure where
     run p@(WHNF _ _) = go p
       where

criterion.cabal

@@ -1,5 +1,5 @@
 name:           criterion
-version:        0.4.0
+version:        0.4.1.0
 synopsis:       Robust, reliable performance measurement and analysis
 license:        BSD3
 license-file:   LICENSE