cli/Hcompta/Lib/Control/Monad.hs

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