Merge pull request #23 from MichaelXavier/writer-misc

Add execWriterT

Author: paf31

docs/Module.md

@@ -667,9 +667,9 @@
 
 ### Values
 
-    evalStateT :: forall s m a. (Monad m) => StateT s m a -> s -> m a
+    evalStateT :: forall s m a. (Apply m) => StateT s m a -> s -> m a
 
-    execStateT :: forall s m a. (Monad m) => StateT s m a -> s -> m s
+    execStateT :: forall s m a. (Apply m) => StateT s m a -> s -> m s
 
     liftCallCCState :: forall s m a b. (((Tuple a s -> m (Tuple b s)) -> m (Tuple a s)) -> m (Tuple a s)) -> ((a -> StateT s m b) -> StateT s m a) -> StateT s m a
 
@@ -779,6 +779,8 @@
 
 ### Values
 
+    execWriterT :: forall w m a. (Apply m) => WriterT w m a -> m w
+
     liftCallCCWriter :: forall w m a b. (Monoid w) => (((Tuple a w -> m (Tuple b w)) -> m (Tuple a w)) -> m (Tuple a w)) -> ((a -> WriterT w m b) -> WriterT w m a) -> WriterT w m a
 
     liftCatchWriter :: forall w m e a. (m (Tuple a w) -> (e -> m (Tuple a w)) -> m (Tuple a w)) -> WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a

src/Control/Monad/State/Trans.purs

@@ -13,11 +13,11 @@ newtype StateT s m a = StateT (s -> m (Tuple a s))
 runStateT :: forall s m a. StateT s m a -> s -> m (Tuple a s)
 runStateT (StateT s) = s
 
-evalStateT :: forall s m a. (Monad m) => StateT s m a -> s -> m a
-evalStateT m s = runStateT m s >>= \(Tuple x _) -> return x
+evalStateT :: forall s m a. (Apply m) => StateT s m a -> s -> m a
+evalStateT m s = fst <$> runStateT m s
 
-execStateT :: forall s m a. (Monad m) => StateT s m a -> s -> m s
-execStateT m s = runStateT m s >>= \(Tuple _ s) -> return s
+execStateT :: forall s m a. (Apply m) => StateT s m a -> s -> m s
+execStateT m s = snd <$> runStateT m s
 
 mapStateT :: forall s m1 m2 a b. (m1 (Tuple a s) -> m2 (Tuple b s)) -> StateT s m1 a -> StateT s m2 b
 mapStateT f m = StateT $ f <<< runStateT m

src/Control/Monad/Writer/Trans.purs

@@ -13,6 +13,9 @@ newtype WriterT w m a = WriterT (m (Tuple a w))
 runWriterT :: forall w m a. WriterT w m a -> m (Tuple a w)
 runWriterT (WriterT x) = x
 
+execWriterT :: forall w m a. (Apply m) => WriterT w m a -> m w
+execWriterT m = snd <$> runWriterT m
+
 mapWriterT :: forall w1 w2 m1 m2 a b. (m1 (Tuple a w1) -> m2 (Tuple b w2)) -> WriterT w1 m1 a -> WriterT w2 m2 b
 mapWriterT f m = WriterT $ f (runWriterT m)