TFHOE/Lib/Control/Monad.hs

   1 module TFHOE.Lib.Control.Monad where
   2
   3 import Control.Applicative (Applicative(..))
   4 import Control.Monad (Monad(..), (=<<), liftM2, liftM3, liftM4, join)
   5 import Data.Bool
   6 import Data.Maybe (Maybe(..), maybe)
   7
   8 -- * 'Monad'ic utilities
   9
  10 -- | Perform some operation on 'Just', given the field inside the 'Just'.
  11 whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m ()
  12 whenJust mg f = maybe (pure ()) f mg
  13
  14 -- | Like 'when', but where the test can be 'Monad'-ic.
  15 whenM :: Monad m => m Bool -> m () -> m ()
  16 whenM b t = ifM b t (return ())
  17
  18 -- | Like 'unless', but where the test can be 'Monad'-ic.
  19 unlessM :: Monad m => m Bool -> m () -> m ()
  20 unlessM b = ifM b (return ())
  21
  22 -- | Like @if@, but where the test can be 'Monad'-ic.
  23 ifM :: Monad m => m Bool -> m a -> m a -> m a
  24 ifM b t f = do b' <- b; if b' then t else f
  25
  26 -- | Like 'liftM' but 'join' the result of the lifted function.
  27 liftMJoin :: Monad m => (a -> m b) -> m a -> m b
  28 liftMJoin = (=<<)
  29
  30 -- | Like 'liftM2' but 'join' the result of the lifted function.
  31 liftM2Join :: Monad m => (a -> b -> m c) -> m a -> m b -> m c
  32 liftM2Join f ma mb = join (liftM2 f ma mb)
  33
  34 -- | Like 'liftM3' but 'join' the result of the lifted function.
  35 liftM3Join :: Monad m => (a -> b -> c -> m d) -> m a -> m b -> m c -> m d
  36 liftM3Join f ma mb mc = join (liftM3 f ma mb mc)
  37
  38 -- | Like 'liftM3' but 'join' the result of the lifted function.
  39 liftM4Join :: Monad m => (a -> b -> c -> d -> m e) -> m a -> m b -> m c -> m d -> m e
  40 liftM4Join f ma mb mc md = join (liftM4 f ma mb mc md)