Haskell Data Analysis Cookbook

Mapping over a list in parallel

In this recipe, we will be applying the map function in parallel. Given a list of values, we will be using multiple threads to apply a function over each value.

How to do it…

1. Import the parallel strategies as follows:

   import Control.Parallel.Strategies

2. Map over a list using the rdeepseq strategy using the following code snippet:

   main = do
     let results = 
               (parMap rdeepseq (^10) [10^10..10^10+10000]) :: [Int]
     print results

3. The first few characters of the printed output are shown here after compiling and running the code as follows:
4. Compile the code with the threaded and rtsopts flags enabled as follows:

   $ ghc -O2 --make Main.hs -threaded -rtsopts
   

5. Run the code by specifying the number of cores as follows:

   $ ./Main +RTS -N2 ...