Type error using Criterion

Question

I read the documentation and some articles that talk about the package, but I'm new to Haskell and did not understand much but I tried ....

Below is what I did:

module Main where  
{-# LANGUAGE BangPatterns #-}   
import Control.Parallel(par,pseq)  
import Control.Exception  
import Data.List  
import IO  
import Data.Char  
import Criterion.Main (defaultMain, bench)  

learquivo :: FilePath -> IO ([[Int]])  
learquivo "mkList1.txt"  = do   
    conteudo <- readFile "mkList1.txt" 
    return (read conteudo) 


main = defaultMain [  
    bench "map sort learquivo" $ \n -> map sort learquivo
    ]

As it did the following error occurred:

Couldn't match expected type [[a]]
       against inferred type FilePath -> IO [[Int]]

Answer 1

The problem is this: map sort learquivo

sort expects a list, and so map sort expects a list of lists ([[a]]), whereas the type of learquivo is of type FilePath -> IO [[Int]].

You probably want something like:

main = do
    contents <- learquivo "mkList1.txt"
    defaultMain [
       bench "map sort learquivo" $ \n -> map sort contents
    ]

There are various things in your code that could be cleaned up, but that should get you going.

Answer 2

Just so you have how I usually run it, using the nf or whnf functions, I'll give my code:

import Data.List
import Criterion.Main

main :: IO ()
main = do
   -- content <- learquivo "mkList1.txt"  
   let content = [ [big, big - step.. 0] | big <- [1000..1010], step <- [1..5]] :: [[Int]]
   defaultMain
        [ bench "benchmark-name" (nf (map sort) content)]

EDIT: If you like this then also give plotting a try:

module Main where

import Data.List
import Criterion.Main
import Criterion.Config
import Criterion.MultiMap as M

main :: IO ()
main = do
   let myConfig = defaultConfig {
              -- Always display an 800x600 window with curves.
              cfgPlot = M.singleton KernelDensity (Window 800 600)
              }
   let content = [ [big, big-step.. 0] | big <- [1000..1010], step <- [1..5]] :: [[Int]]
   defaultMainWith myConfig (return ())
        [ bench "benchmark-name" (nf (map sort) content)]