Util.hs

   1 -- This file is part of htalkat
   2 -- Copyright (C) 2021 Martin Bays <mbays@sdf.org>
   3 --
   4 -- This program is free software: you can redistribute it and/or modify
   5 -- it under the terms of version 3 of the GNU General Public License as
   6 -- published by the Free Software Foundation, or any later version.
   7 --
   8 -- You should have received a copy of the GNU General Public License
   9 -- along with this program.  If not, see http://www.gnu.org/licenses/.
  10
  11 {-# LANGUAGE Safe #-}
  12
  13 module Util where
  14 import           Control.Monad (unless, when)
  15
  16 -- nice tip from one joeyh:
  17 whenM,unlessM,(>>?),(>>!) :: Monad m => m Bool -> m () -> m ()
  18 whenM c a = c >>= flip when a
  19 unlessM c a = c >>= flip unless a
  20 (>>?) = whenM
  21 (>>!) = unlessM
  22 -- same precedence as ($), allowing e.g. foo bar >>! error $ "failed " ++ meep
  23 infixr 0 >>?
  24 infixr 0 >>!
  25
  26 maybeToEither :: e -> Maybe a -> Either e a
  27 maybeToEither e = maybe (Left e) Right
  28
  29 eitherToMaybe :: Either e a -> Maybe a
  30 eitherToMaybe (Left _)  = Nothing
  31 eitherToMaybe (Right a) = Just a