Add argument to set num of threads, default 1

Author: jneira

exe/Arguments.hs

@@ -36,7 +36,7 @@ data Arguments = Arguments
     -- them to just change the name of the exe and still work.
     , argsDebugOn       :: Bool
     , argsLogFile       :: Maybe String
-
+    , argsThread        :: Int
     }
 
 getArguments :: String -> IO Arguments
@@ -73,6 +73,13 @@ arguments exeName = Arguments
           <> metavar "LOGFILE"
           <> help "File to log to, defaults to stdout"
            ))
+      <*> option auto
+           (short 'j'
+          <> help "Number of threads (0: automatic)"
+          <> metavar "NUM"
+          <> value 1
+          <> showDefault
+           )
 
 -- ---------------------------------------------------------------------
 -- Set the GHC libdir to the nix libdir if it's present.