[Haskell-cafe] shake and cmd argument dependency

[Peter Simons]

Hi,

 > How can I teach shake to rebuild a rules when
 > the argument of the cmd change?

wrap the arguments that are subject to change into
an oracle to detect changes and to re-run all
actions that depend on the value:

{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE TypeFamilies #-}

import Development.Shake
import Development.Shake.Classes

newtype GetCmdlineArgs = GetCmdlineArgs () deriving (Show,Typeable,Eq,Hashable,Binary,NFData)
type instance RuleResult GetCmdlineArgs = String

main :: IO ()
main =
  shake shakeOptions $ do
  want ["foo.txt"]

  getCmdlineArgs <- addOracle $ \(GetCmdlineArgs ()) -> 
    return "This is a test!"

  "*.txt" %> \out -> do
    args <- getCmdlineArgs (GetCmdlineArgs ())
    command [FileStdout out] "echo" [args]

Best regards,
Peter