Parallelize fetching deps

elm2nix.cabal

@@ -30,6 +30,7 @@ library
       src
   build-depends:
       base >= 4.7 && < 5
+    , async
     , elm-package
     , elm-compiler
     , directory

elm2nix/Main.hs

@@ -6,12 +6,15 @@ import qualified Control.Monad (join)
 import Data.Version (showVersion)
 import Data.String.Here
 import Options.Applicative
+import System.IO
 import qualified Lib
 import qualified Paths_elm2nix as This
 import qualified Text.PrettyPrint.ANSI.Leijen as PP
 
 main :: IO ()
 main = do
+  hSetBuffering stdout LineBuffering
+  hSetBuffering stderr LineBuffering
   cmd <- getOpts
   case cmd of
     Convert -> Lib.convert

src/Lib.hs

@@ -5,7 +5,7 @@ module Lib
     , init'
     ) where
 
-import Control.Monad (mapM)
+import Control.Concurrent.Async
 import Control.Monad.Except (liftIO, throwError)
 import Data.List (intercalate)
 import qualified Data.Text as Text
@@ -59,7 +59,7 @@ generateDefault = do
 
 solveDependencies :: Manager.Manager ()
 solveDependencies = do
-  liftIO $ hPutStrLn stderr "Resolving elm-package.json dependencies into elm-stuff/exact-dependencies.json ..."
+  liftIO $ hPutStrLn stderr "Resolving elm-package.json dependencies into Nix ..."
 
   desc <- readDescription
   newSolution <- Solver.solve (Desc.elmVersion desc) (Desc.dependencies desc)
@@ -69,7 +69,7 @@ solveDependencies = do
   liftIO $ hPutStrLn stderr "Prefetching tarballs and computing sha256 hashes ..."
 
   let solL = Map.toList newSolution
-  sources <- liftIO $ mapM Prefetch.prefetchURL solL
+  sources <- liftIO $ mapConcurrently Prefetch.prefetchURL solL
 
   liftIO $ putStrLn $ generateNixSources sources