PureScript by Example: Chapter 12 (Callback Hell) exercise 12.8.1

ParallelConcat.purs

module ParallelConcat where

import Prelude (Unit, (<<<), ($), bind)

import Types (Async)

import Control.Monad.Except.Trans (ExceptT, mapExceptT)
import Control.Parallel (inParallel, runParallel)

import Data.Foldable (fold)
import Data.Traversable (class Traversable, traverse)

import Files (ErrorCode, FilePath, FS, readFileContEx, writeFileContEx)

concatenateMany :: forall eff t. Traversable t => t FilePath -> FilePath -> ExceptT ErrorCode (Async (fs :: FS | eff)) Unit
concatenateMany srcs trg = do
    c <- mapExceptT runParallel $ traverse (mapExceptT inParallel <<< readFileContEx) srcs
    writeFileContEx trg (fold c)