1 files changed, 26 insertions, 0 deletions
diff --git a/src/Utils/Monad.hs b/src/Utils/Monad.hs
new file mode 100644
index 0000000..3c1ad17
--- /dev/null
+++ b/src/Utils/Monad.hs
@@ -0,0 +1,26 @@
+{-|
+Module      : Utils.Monad
+Copyright   : (c) UU, 2019
+License     : MIT
+Maintainer  : Tom Smeding
+Stability   : experimental
+Portability : POSIX, macOS, Windows
+
+Some useful functions lifted to monadic actions.
+-}
+module Utils.Monad where
+
+
+-- | If the boolean resolves to True, returns the first argument, else the
+-- second.
+ifM :: Monad m => m Bool -> m a -> m a -> m a
+ifM b t e = b >>= \b' -> if b' then t else e
+
+-- | Runs the monadic action only if the boolean resolves to True.
+whenM :: Monad m => m Bool -> m () -> m ()
+whenM b t = ifM b t (return ())
+
+-- | whenJust m a = when (isJust m) (a (fromJust m)), but with less
+-- fromJust.
+whenJust :: Monad m => Maybe a -> (a -> m ()) -> m ()
+whenJust = flip (maybe (return ()))