diohsc-0.1.1: Util.hs

-- This file is part of Diohsc
-- Copyright (C) 2020 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 TupleSections #-}
{-# LANGUAGE Safe #-}

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

-- 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 >>!

-- |Probably I'm missing some nice way to do these with prelude...
mapFst :: (a -> c) -> (a,b) -> (c,b)
mapFst f (x,y) = (f x,y)
mapSnd :: (b -> c) -> (a,b) -> (a,c)
mapSnd f (x,y) = (x,f y)

mapFstF :: Functor f => (a -> f c) -> (a,b) -> f (c,b)
mapFstF f (x,y) = (,y) <$> f x
mapSndF :: Functor f => (b -> f c) -> (a,b) -> f (a,c)
mapSndF f (x,y) = (x,) <$> f y

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