Propellor monad is a Reader for HostAttr

So far, the hostname is only used to improve a message in withPrivData,
but I anticipate using HostAttr for a lot more.

1 files changed, 34 insertions, 1 deletions

diff --git a/Propellor/Types.hs b/Propellor/Types.hs
index 3be10d3f..b1632923 100644
--- a/Propellor/Types.hs
+++ b/Propellor/Types.hs
@@ -1,20 +1,53 @@
+{-# LANGUAGE PackageImports #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
 module Propellor.Types where
 
 import Data.Monoid
+import Control.Applicative
 import System.Console.ANSI
+import "mtl" Control.Monad.Reader
+import "MonadCatchIO-transformers" Control.Monad.CatchIO
 
 type HostName = String
 type GroupName = String
 type UserName = String
 
+-- | The core data type of Propellor, this reprecents a property
+-- that the system should have, and an action to ensure it has the
+-- property.
 data Property = Property
 	{ propertyDesc :: Desc
 	-- | must be idempotent; may run repeatedly
-	, propertySatisfy :: IO Result
+	, propertySatisfy :: Propellor Result
 	}
 
+-- | A property that can be reverted.
 data RevertableProperty = RevertableProperty Property Property
 
+-- | Propellor's monad provides read-only access to attributes of the
+-- system.
+newtype Propellor a = Propellor { runWithHostAttr :: ReaderT HostAttr IO a }
+	deriving
+		( Monad
+		, Functor
+		, Applicative
+		, MonadReader HostAttr 
+		, MonadIO
+		, MonadCatchIO
+		)
+
+-- | The attributes of a system. For example, its hostname.
+newtype HostAttr = HostAttr
+	{ _hostname :: HostName
+	}
+
+mkHostAttr :: HostName -> HostAttr
+mkHostAttr = HostAttr 
+
+getHostName :: Propellor HostName
+getHostName = asks _hostname
+
 class IsProp p where
 	-- | Sets description.
 	describe :: p -> Desc -> p