yjtools-0.1: Control/Monad/Utils.hs

module Control.Monad.Utils (
  ifM
, whenM
, unlessM
, doWhile_
, doWhile
) where

import Control.Monad         (when, unless)

doWhile :: Monad m => a -> (a -> m (a, Bool)) -> m a
doWhile i act = do (r, p) <- act i
                   if p then doWhile r act
		        else return r

doWhile_ :: Monad m => m Bool -> m ()
doWhile_ act = do p <- act
                  when p $ doWhile_ act

ifM :: Monad m => m Bool -> m a -> m a -> m a
ifM p t e = do b <- p
               if b then t else e

whenM, unlessM :: Monad m => m Bool -> m () -> m ()
whenM p t   = p >>= flip when t
unlessM p e = p >>= flip unless e