More applicative

test.hs

@@ -1,4 +1,4 @@
-import Control.Monad
+import Control.Applicative
 import Nock5K.Parse
 import Nock5K.Spec
 import Test.QuickCheck
@@ -10,22 +10,19 @@ main = mapM_ (\(s,a) -> printf "%-25s: " s >> a) tests
 instance Arbitrary Noun where
   arbitrary = do coin <- arbitrary
                  if coin
-                   then liftM (Atom . abs) arbitrary
-                   else do a <- arbitrary
-                           b <- arbitrary
-                           return $ a :- b
+                   then (Atom . abs) <$> arbitrary
+                   else (:-) <$> arbitrary <*> arbitrary
 
-prop_parse_show n = n == ps n
-  where ps n = case parse noun "" (show n) of
-                 Left e -> error "parse"
-                 Right n -> n
+parsenoun n = case parse noun "" n of
+  Left e -> error "parse"
+  Right n -> n
+
+prop_parse_show n = n == (parsenoun . show) n
 
 prop_dec a' = nock (Atom (a + 1) :- dec) == Atom a
   where
     ds = "[8 [1 0] 8 [1 6 [5 [0 7] 4 0 6] [0 6] 9 2 [0 2] [4 0 6] 0 7] 9 2 0 1]"
-    dec = case parse noun "" ds of
-            Left e -> error "parse"
-            Right n -> n
+    dec = parsenoun ds
     a = abs a'
 
 prop_6_is_if a' b' = nock (ifs $ Atom 0) == Atom (a + 1) && nock (ifs $ Atom 1) == Atom b