module Toolbox
       ( -- Applicative
         pure,

         -- Monad
         (>>=), (>=>),

         -- local
         (<>),
         (<!>),(|?),
         clo, rclo, mclo, mrclo,
         just
       )
       where


import Control.Monad       ((>>=),(>=>),MonadPlus(mplus,mzero),mfilter)
import Control.Applicative (pure)

import Data.Foldable

-- OR

infixr 6 <>
(<>) :: (MonadPlus m) => (a -> m b) -> (a -> m b) -> (a -> m b)
(f <> g) x = f x `mplus` g x

-- SHORT CIRCUIT OR

infixr 6 <!>
(<!>) :: (MonadPlus m, Foldable m) => (a -> m b) -> (a -> m b) -> (a -> m b)
(f <!> g) x = let fx = f x in if null fx then g x else fx 

-- VALUE FILTER
                       
infixl 4 |?
(|?) :: (MonadPlus m) => (a -> m b) -> (b -> Bool) -> (a -> m b)
f |? g  = mfilter g . f



clo,mclo,rclo,mrclo:: (MonadPlus m, Foldable m) => (a -> m a) -> a -> m a
clo f     = f >=> ( pure <> clo f )
rclo f    = pure <> clo f
mrclo f = (f >=> mrclo f) <!> pure
mclo f  = f >=> mrclo f


-- INPUT: Function f returning element of a list or fails if list empty
-- OUTPUT: Function returning the list containing the f value or empty list
-- ex: the maximum, the head, the last, e.t.c

-- the :: ([a] -> b) -> ([a] -> [b])
-- (the f) [] = []
-- (the f) xs = [f xs]

just :: ([a] -> b) -> ([a] -> [b])
(just f) [] = []
(just f) xs = [f xs]

its :: (a->b) -> ([a]->b)
its f = f.head

their :: (a->b) -> ([a]->[b])
their = map