From be02ef96aa89a6af554a622f266d700ac0c98fdf Mon Sep 17 00:00:00 2001
From: Joey Hess <joeyh@debian.org>
Date: Fri, 11 Apr 2014 01:19:05 -0400
Subject: propellor (0.3.0) unstable; urgency=medium

  * ipv6to4: Ensure interface is brought up automatically on boot.
  * Enabling unattended upgrades now ensures that cron is installed and
    running to perform them.
  * Properties can be scheduled to only be checked after a given time period.
  * Fix bootstrapping of dependencies.
  * Fix compilation on Debian stable.
  * Include security updates in sources.list for stable and testing.
  * Use ssh connection caching, especially when bootstrapping.
  * Properties now run in a Propellor monad, which provides access to
    attributes of the host.

# imported from the archive
---
 Utility/Monad.hs | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 Utility/Monad.hs

(limited to 'Utility/Monad.hs')

diff --git a/Utility/Monad.hs b/Utility/Monad.hs
new file mode 100644
index 00000000..1ba43c5f
--- /dev/null
+++ b/Utility/Monad.hs
@@ -0,0 +1,69 @@
+{- monadic stuff
+ -
+ - Copyright 2010-2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.Monad where
+
+import Data.Maybe
+import Control.Monad
+
+{- 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) = ifM (p x) (return $ Just x , firstM p xs)
+
+{- Runs the action on values from the list until it succeeds, returning
+ - its result. -}
+getM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b)
+getM _ [] = return Nothing
+getM p (x:xs) = maybe (getM p xs) (return . Just) =<< p x
+
+{- Returns true if any value in the list satisfies the predicate,
+ - stopping once one is found. -}
+anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool
+anyM p = liftM isJust . firstM p
+
+allM :: Monad m => (a -> m Bool) -> [a] -> m Bool
+allM _ [] = return True
+allM p (x:xs) = p x <&&> allM p xs
+
+{- Runs an action on values from a list until it succeeds. -}
+untilTrue :: Monad m => [a] -> (a -> m Bool) -> m Bool
+untilTrue = flip anyM
+
+{- if with a monadic conditional. -}
+ifM :: Monad m => m Bool -> (m a, m a) -> m a
+ifM cond (thenclause, elseclause) = do
+	c <- cond
+	if c then thenclause else elseclause
+
+{- short-circuiting monadic || -}
+(<||>) :: Monad m => m Bool -> m Bool -> m Bool
+ma <||> mb = ifM ma ( return True , mb )
+
+{- short-circuiting monadic && -}
+(<&&>) :: Monad m => m Bool -> m Bool -> m Bool
+ma <&&> mb = ifM ma ( mb , return False )
+
+{- Same fixity as && and || -}
+infixr 3 <&&>
+infixr 2 <||>
+
+{- Runs an action, passing its value to an observer before returning it. -}
+observe :: Monad m => (a -> m b) -> m a -> m a
+observe observer a = do
+	r <- a
+	_ <- observer r
+	return r
+
+{- b `after` a runs first a, then b, and returns the value of a -}
+after :: Monad m => m b -> m a -> m a
+after = observe . const
+
+{- do nothing -}
+noop :: Monad m => m ()
+noop = return ()
-- 
cgit v1.3-2-g0d8e