Haskell Criterion Usage Error

Question

The following code named fib.hs

import Criterion.Main (defaultMain)
fibZ = 1:1:zipWith (+) fibZ (tail fibZ)
main = defaultMain [
         bench "fibZ 10" $ \n -> fibZ (10+n-n)
       ]

errors with

fib.hs:45:10: Not in scope: `bench'

What is wrong? I have borrowed this example from here.

Answer 1

The library has changed since that blog post was written. Now you should write:

 import Criterion.Main

 fib :: Int -> Int
 fib 0 = 0
 fib 1 = 1
 fib n = fib (n-1) + fib (n-2)

 main = defaultMain [
        bgroup "fib" [ bench "fib 10" $ B fib 10
                     , bench "fib 35" $ B fib 35
                     , bench "fib 37" $ B fib 37
                     ]
                    ]

This was taken directly from the "Running benchmarks" section of the Hackage documentation for Criterion.Main.

Answer 2

Use

import Criterion.Main

instead of

import Criterion.Main (defaultMain)

The function bench from Criterion.Main is not in scope because you're importing only defaultMain. Using bgroup is not necessary.

Here's a full working example:

import Criterion.Main

fib :: Int -> Int
fib 0 = 0
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

main = defaultMain [
         bench "fib 10" $ nf fib 10
       , bench "fib 30" $ nf fib 30
       , bench "fib 35" $ nf fib 35
       ]

If you're wondering what these nf thingies are for, look at this section of the documentation.