htalkat-0.1.1: Util.hs

-- This file is part of htalkat
-- Copyright (C) 2021 Martin Bays <mbays@sdf.org>
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of version 3 of the GNU General Public License as
-- published by the Free Software Foundation, or any later version.
--
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see http://www.gnu.org/licenses/.

{-# LANGUAGE Safe #-}

module Util where
import           Control.Monad (unless, when)

-- nice tip from one joeyh:
whenM,unlessM,(>>?),(>>!) :: Monad m => m Bool -> m () -> m ()
whenM c a = c >>= flip when a
unlessM c a = c >>= flip unless a
(>>?) = whenM
(>>!) = unlessM
-- same precedence as ($), allowing e.g. foo bar >>! error $ "failed " ++ meep
infixr 0 >>?
infixr 0 >>!

maybeToEither :: e -> Maybe a -> Either e a
maybeToEither e = maybe (Left e) Right

eitherToMaybe :: Either e a -> Maybe a
eitherToMaybe (Left _)  = Nothing
eitherToMaybe (Right a) = Just a