From 4650b6c9f30c3992cb2c85727089662d50c46814 Mon Sep 17 00:00:00 2001
From: Eric Easley <escalier@riseup.net>
Date: Wed, 18 Mar 2015 09:36:44 -0400
Subject: [PATCH 1/2] Added filterM

---
 README.md              | 7 +++++++
 src/Control/Monad.purs | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/README.md b/README.md
index 93a7a0e..2486b4b 100644
--- a/README.md
+++ b/README.md
@@ -297,6 +297,13 @@ unless :: forall m. (Monad m) => Boolean -> m Unit -> m Unit
 ```
 
 
+#### `filterM`
+
+``` purescript
+filterM :: forall a m. (Monad m) => (a -> m Boolean) -> [a] -> m [a]
+```
+
+
 
 ## Module Control.MonadPlus
 
diff --git a/src/Control/Monad.purs b/src/Control/Monad.purs
index 639bfd5..50a778b 100644
--- a/src/Control/Monad.purs
+++ b/src/Control/Monad.purs
@@ -18,3 +18,12 @@ when false _ = return unit
 unless :: forall m. (Monad m) => Boolean -> m Unit -> m Unit
 unless false m = m
 unless true _ = return unit
+
+filterM :: forall a m. (Monad m) => (a -> m Boolean) -> [a] -> m [a]
+filterM _ [] = return []
+filterM p (x:xs) = do
+  b <- p x
+  xs' <- filterM p xs
+  return $ if b
+           then x : xs'
+           else xs'

From b17994e1b213f4364e6595090a06ab1570437f18 Mon Sep 17 00:00:00 2001
From: Eric Easley <escalier@riseup.net>
Date: Wed, 18 Mar 2015 15:40:47 -0400
Subject: [PATCH 2/2] Added filterM comment

---
 README.md              | 6 ++++++
 src/Control/Monad.purs | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/README.md b/README.md
index 2486b4b..8258e5e 100644
--- a/README.md
+++ b/README.md
@@ -303,6 +303,12 @@ unless :: forall m. (Monad m) => Boolean -> m Unit -> m Unit
 filterM :: forall a m. (Monad m) => (a -> m Boolean) -> [a] -> m [a]
 ```
 
+Filter where the predicate returns a monadic Boolean. For example: 
+
+```purescript
+powerSet :: forall a. [a] -> [[a]]
+powerSet = filterM (const [true, false])
+```
 
 
 ## Module Control.MonadPlus
diff --git a/src/Control/Monad.purs b/src/Control/Monad.purs
index 50a778b..35618d0 100644
--- a/src/Control/Monad.purs
+++ b/src/Control/Monad.purs
@@ -19,6 +19,12 @@ unless :: forall m. (Monad m) => Boolean -> m Unit -> m Unit
 unless false m = m
 unless true _ = return unit
 
+-- | Filter where the predicate returns a monadic Boolean. For example: 
+-- |
+-- | ```purescript
+-- | powerSet :: forall a. [a] -> [[a]]
+-- | powerSet = filterM (const [true, false])
+-- | ```
 filterM :: forall a m. (Monad m) => (a -> m Boolean) -> [a] -> m [a]
 filterM _ [] = return []
 filterM p (x:xs) = do