diff options
author | 2011-08-28 15:46:49 -0400 | |
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committer | 2011-08-28 15:46:49 -0400 | |
commit | 999d5df90b013a7cc8a390c940785118400faf8a (patch) | |
tree | 82b9e2ab8c00e32f88c5878b06b1301413b51e53 /Utility.hs | |
parent | b26ee162f33858aa4ef82fbe3d56eecc00590755 (diff) |
factor out firstM and anyM
Control.Monad.Loops has these, but has no Debian package yet.
Diffstat (limited to 'Utility.hs')
-rw-r--r-- | Utility.hs | 28 |
1 files changed, 22 insertions, 6 deletions
diff --git a/Utility.hs b/Utility.hs index 451b1b44f..ce1736348 100644 --- a/Utility.hs +++ b/Utility.hs @@ -16,7 +16,9 @@ module Utility ( dirContents, myHomeDir, catchBool, - inPath + inPath, + firstM, + anyM ) where import IO (bracket) @@ -29,6 +31,8 @@ import System.FilePath import System.Directory import Foreign (complement) import Utility.Path +import Data.Maybe +import Control.Monad (liftM) {- A version of hgetContents that is not lazy. Ensures file is - all read before it gets closed. -} @@ -96,11 +100,23 @@ myHomeDir = do catchBool :: IO Bool -> IO Bool catchBool = flip catch (const $ return False) +{- Return the first value from a list, if any, satisfying the given + - predicate -} +firstM :: (Monad m) => (a -> m Bool) -> [a] -> m (Maybe a) +firstM _ [] = return Nothing +firstM p (x:xs) = do + q <- p x + if q + then return (Just x) + else firstM p xs + +{- Returns true if any value in the list satisfies the preducate, + - stopping once one is found. -} +anyM :: (Monad m) => (a -> m Bool) -> [a] -> m Bool +anyM p = liftM isJust . firstM p + {- Checks if a command is available in PATH. -} inPath :: String -> IO Bool -inPath command = search =<< getSearchPath +inPath command = getSearchPath >>= anyM indir where - search [] = return False - search (d:ds) = do - e <- doesFileExist $ d </> command - if e then return True else search ds + indir d = doesFileExist $ d </> command |