# HG changeset patch
# User Yasutaka Higa <e115763@ie.u-ryukyu.ac.jp>
# Date 1409626133 -32400
# Node ID 41c71f67c103854f6dbb05693f09ca332cc03b4f
# Parent  6e0285628ead8dae43500b2d6c681d8734abec85
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diff -r 6e0285628ead -r 41c71f67c103 similer.hs
--- a/similer.hs	Tue Sep 02 11:27:49 2014 +0900
+++ b/similer.hs	Tue Sep 02 11:48:53 2014 +0900
@@ -1,4 +1,3 @@
-{-# LANGUAGE UndecidableInstances #-}
 data Similer a b = Similer a (a -> b) b
 
 instance Functor (Similer a) where
@@ -22,10 +21,10 @@
 plusTwo :: Int -> Int
 plusTwo x = x + 2
 
-same :: Eq b => Similer a b -> b
-same (Similer x f y) = if (f x) == y then y else undefined
+same :: (Show b, Eq b) => Similer a b -> b
+same (Similer x f y) = if (f x) == y then y else (error ("not same :" ++ show y))
 
-similer :: Eq b => (a -> b) -> (a -> b) -> a -> b
+similer :: (Show b, Eq b) => (a -> b) -> (a -> b) -> a -> b
 similer f g x = same $ Similer x g (f x)