1 files changed, 5 insertions, 2 deletions
diff --git a/System/Random/Shuffle.hs b/System/Random/Shuffle.hs
index d26361f..435f083 100644
--- a/System/Random/Shuffle.hs
+++ b/System/Random/Shuffle.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE NoImplicitPrelude #-}
 {-# OPTIONS_GHC -funbox-strict-fields #-}
 
 -- |
@@ -24,6 +26,7 @@ module System.Random.Shuffle
   )
 where
 
+import Alpha
 import Control.Monad
   ( liftM2,
   )
@@ -70,7 +73,7 @@ shuffle elements = shuffleTree (buildTree elements)
     shuffleTree (Leaf e) [] = [e]
     shuffleTree tree (r : rs) =
       let (b, rest) = extractTree r tree in b : shuffleTree rest rs
-    shuffleTree _ _ = error "[shuffle] called with lists of different lengths"
+    shuffleTree _ _ = panic "[shuffle] called with lists of different lengths"
     -- Extracts the n-th element from the tree and returns
     -- that element, paired with a tree with the element
     -- deleted.
@@ -86,7 +89,7 @@ shuffle elements = shuffleTree (buildTree elements)
         let (e, l') = extractTree n l in (e, Node (c - 1) l' r)
       | otherwise =
         let (e, r') = extractTree (n - cl) r in (e, Node (c - 1) l r')
-    extractTree _ _ = error "[extractTree] impossible"
+    extractTree _ _ = panic "[extractTree] impossible"
 
 -- | Given a sequence (e1,...en) to shuffle, its length, and a random
 --  generator, compute the corresponding permutation of the input