Util.hs

   1 -- This file is part of Diohsc
   2 -- Copyright (C) 2020 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
  12 {-# LANGUAGE Safe #-}
  13
  14 module Util where
  15 import           Control.Monad (unless, when)
  16
  17 -- nice tip from one joeyh:
  18 whenM,unlessM,(>>?),(>>!) :: Monad m => m Bool -> m () -> m ()
  19 whenM c a = c >>= flip when a
  20 unlessM c a = c >>= flip unless a
  21 (>>?) = whenM
  22 (>>!) = unlessM
  23 -- same precedence as ($), allowing e.g. foo bar >>! error $ "failed " ++ meep
  24 infixr 0 >>?
  25 infixr 0 >>!
  26
  27 maybeToEither :: e -> Maybe a -> Either e a
  28 maybeToEither e = maybe (Left e) Right