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diff --git a/compiler/src/Utils.hs b/compiler/src/Utils.hs
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+-- ldgallery - A static generator which turns a collection of tagged
+--             pictures into a searchable web gallery.
+--
+-- Copyright (C) 2019  Pacien TRAN-GIRARD
+--
+-- This program is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU Affero General Public License as
+-- published by the Free Software Foundation, either version 3 of the
+-- License, or (at your option) any later version.
+--
+-- This program is distributed in the hope that it will be useful,
+-- but WITHOUT ANY WARRANTY; without even the implied warranty of
+-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+-- GNU Affero General Public License for more details.
+--
+-- You should have received a copy of the GNU Affero General Public License
+-- along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+
+module Utils
+  ( conj, neg
+  , unique
+  , passthrough
+  ) where
+
+
+import qualified Data.List
+import qualified Data.Set
+
+
+-- predicates
+
+conj :: (a -> Bool) -> (a -> Bool) -> a -> Bool
+conj p q x = (p x) && (q x)
+
+neg :: (a -> Bool) -> a -> Bool
+neg p x = not (p x)
+
+
+-- lists
+
+unique :: Ord a => [a] -> [a]
+unique = Data.Set.toList . Data.Set.fromList
+
+
+-- monads
+
+passthrough :: Monad m => (a -> m b) -> a -> m a
+passthrough f a = return a >>= f >>= \_ -> return a