Merge pull request #20 from jacereda/master

Fix toEnum for (Maybe a)

Author: garyb

src/Data/Enum.purs

@@ -193,12 +193,8 @@ instance boundedEnumOrdering :: BoundedEnum Ordering where
 
 instance boundedEnumMaybe :: BoundedEnum a => BoundedEnum (Maybe a) where
   cardinality = Cardinality $ unwrap (cardinality :: Cardinality a) + 1
-  toEnum = to cardinality
-    where
-    to :: Cardinality a -> Int -> Maybe (Maybe a)
-    to _ 0 = Nothing
-    to (Cardinality ca) n | n <= ca = Just $ toEnum (n - 1)
-    to _ _ = Nothing
+  toEnum 0 = pure Nothing
+  toEnum n = Just <$> toEnum (n - 1)
   fromEnum Nothing = 0
   fromEnum (Just e) = fromEnum e + 1
 

test/Test/Data/Enum.purs

@@ -7,7 +7,7 @@ import Control.Monad.Eff.Console (CONSOLE, log)
 
 import Data.Enum (class Enum, class BoundedEnum, defaultToEnum, defaultFromEnum,
                   defaultCardinality, enumFromTo, enumFromThenTo, upFrom,
-                  downFrom)
+                  downFrom, toEnum)
 import Data.Maybe (Maybe(..))
 
 import Test.Assert (ASSERT, assert)
@@ -63,3 +63,10 @@ testEnum = do
   assert $ downFrom D == [C, B, A]
   assert $ downFrom B == [      A]
   assert $ downFrom A == [       ]
+
+  log "BoundedEnum (Maybe Boolean)"
+  assert $ toEnum (-1) == Nothing :: Maybe (Maybe Boolean)
+  assert $ toEnum 0 == Just Nothing :: Maybe (Maybe Boolean)
+  assert $ toEnum 1 == Just (Just false) :: Maybe (Maybe Boolean)
+  assert $ toEnum 2 == Just (Just true) :: Maybe (Maybe Boolean)
+  assert $ toEnum 3 == Nothing :: Maybe (Maybe Boolean)