Merge pull request #110 from purescript/modify_

Add modify_

Author: garyb

src/Control/Monad/RWS.purs

@@ -16,7 +16,7 @@ import Prelude
 
 import Control.Monad.Reader.Class (ask, asks, local) as Exports
 import Control.Monad.RWS.Trans (class MonadTrans, RWSResult(..), RWST(..), evalRWST, execRWST, lift, mapRWST, runRWST, withRWST)
-import Control.Monad.State.Class (get, gets, state, put, modify) as Exports
+import Control.Monad.State.Class (get, gets, state, put, modify, modify_) as Exports
 import Control.Monad.Trans.Class (lift) as Exports
 import Control.Monad.Writer.Class (censor, listen, listens, pass, tell) as Exports
 

src/Control/Monad/State.purs

@@ -13,7 +13,7 @@ module Control.Monad.State
 
 import Prelude
 
-import Control.Monad.State.Class (class MonadState, get, gets, modify, put, state)
+import Control.Monad.State.Class (class MonadState, get, gets, modify, modify_, put, state)
 import Control.Monad.State.Trans (class MonadTrans, StateT(..), evalStateT, execStateT, lift, mapStateT, runStateT, withStateT)
 
 import Data.Identity (Identity(..))

src/Control/Monad/State/Class.purs

@@ -40,3 +40,6 @@ put s = state \_ -> Tuple unit s
 -- | value is the new state value.
 modify :: forall s m. MonadState s m => (s -> s) -> m s
 modify f = state \s -> let s' = f s in Tuple s' s'
+
+modify_ :: forall s m. MonadState s m => (s -> s) -> m Unit
+modify_ f = state \s -> Tuple unit (f s)

src/Control/Monad/State/Trans.purs

@@ -15,7 +15,7 @@ import Control.Monad.Cont.Class (class MonadCont, callCC)
 import Control.Monad.Error.Class (class MonadThrow, class MonadError, catchError, throwError)
 import Control.Monad.Reader.Class (class MonadAsk, class MonadReader, ask, local)
 import Control.Monad.Rec.Class (class MonadRec, tailRecM, Step(..))
-import Control.Monad.State.Class (class MonadState, get, gets, modify, put, state)
+import Control.Monad.State.Class (class MonadState, get, gets, modify, modify_, put, state)
 import Control.Monad.Trans.Class (class MonadTrans, lift)
 import Control.Monad.Writer.Class (class MonadWriter, class MonadTell, pass, listen, tell)
 import Control.MonadPlus (class MonadPlus)