Commit 95d2949e authored by Andrey Mokhov's avatar Andrey Mokhov
Browse files

Move Monoid (ReaderT Target Action a) instance to src/Target.hs.

parent 4d70a1e6
{-# LANGUAGE DeriveGeneric, TypeSynonymInstances #-}
{-# LANGUAGE DeriveGeneric, FlexibleInstances #-}
module Target (
Target (..), StageTarget (..), StagePackageTarget (..), FullTarget (..),
Target (..), StageTarget, StagePackageTarget, FullTarget,
stageTarget, stagePackageTarget, fullTarget, fullTargetWithWay,
) where
......@@ -10,6 +10,8 @@ import Stage
import Package
import Builder
import GHC.Generics
import Data.Monoid
import Control.Monad.Reader
-- Target captures all parameters relevant to the current build target:
-- * Stage and Package being built,
......@@ -28,6 +30,14 @@ data Target = Target
deriving (Show, Eq, Generic)
-- If values of type 'a' form a Monoid then we can also derive a Monoid instance
-- for values of type 'ReaderT Target Action a':
-- * the empty computation returns the identity element of the underlying type
-- * two computations can be combined by combining their results
instance Monoid a => Monoid (ReaderT Target Action a) where
mempty = return mempty
mappend = liftM2 mappend
-- StageTarget is a partially constructed Target. Only stage is guaranteed to
-- be assigned.
type StageTarget = Target
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