Enum.range - all elements of an enum, ordered

bower.json

@@ -20,10 +20,14 @@
   "dependencies": {
     "purescript-either": "^3.0.0",
     "purescript-strings": "^3.0.0",
-    "purescript-unfoldable": "^3.0.0"
+    "purescript-unfoldable": "^3.0.0",
+    "purescript-arrays": "matthewleon/purescript-arrays#nonempty"
   },
   "devDependencies": {
     "purescript-assert": "^3.0.0",
     "purescript-console": "^3.0.0"
+  },
+  "resolutions": {
+    "purescript-arrays": "nonempty"
   }
 }

src/Data/Enum/Range.purs

@@ -0,0 +1,30 @@
+module Data.Enum.Range
+  ( Range
+  , range
+  , toNonEmptyArray
+  , cardinalityFromRange
+  , toEnumFromRange
+  ) where
+
+import Prelude
+
+import Data.Array.NonEmpty (NonEmptyArray, fromNonEmpty, index, length)
+import Data.Enum (class Enum, Cardinality(..), upFromIncluding)
+import Data.Maybe (Maybe)
+
+newtype Range a = Range (NonEmptyArray a)
+
+-- smart constructor for Range
+range :: forall a. Bounded a => Enum a => Range a
+range = Range $ fromNonEmpty $ upFromIncluding bottom
+
+toNonEmptyArray :: forall a. Range a -> NonEmptyArray a
+toNonEmptyArray (Range xs) = xs
+
+-- | Runs in `O(1)`
+cardinalityFromRange :: forall a. Range a -> Cardinality a
+cardinalityFromRange = Cardinality <<< length <<< toNonEmptyArray
+
+-- | Runs in `O(1)`
+toEnumFromRange :: forall a. Range a -> Int -> Maybe a
+toEnumFromRange = index <<< toNonEmptyArray

test/Main.purs

@@ -7,6 +7,9 @@ import Control.Monad.Eff.Console (CONSOLE)
 
 import Test.Assert (ASSERT)
 import Test.Data.Enum (testEnum)
+import Test.Data.Enum.Range (testRange)
 
 main :: Eff (console :: CONSOLE, assert :: ASSERT) Unit
-main = testEnum
+main = do
+  testEnum
+  testRange

test/Test/Data/Enum/Range.purs

@@ -0,0 +1,56 @@
+module Test.Data.Enum.Range (testRange) where
+
+import Prelude
+
+import Control.Monad.Eff (Eff)
+import Control.Monad.Eff.Console (CONSOLE, log)
+import Data.Array.NonEmpty (toArray)
+import Data.Enum (class Enum, class BoundedEnum, Cardinality(..), cardinality, defaultFromEnum, toEnum)
+import Data.Enum.Range (Range, range, toNonEmptyArray, cardinalityFromRange, toEnumFromRange)
+import Data.Maybe (Maybe(..))
+import Test.Assert (ASSERT, assert)
+
+data T = A | B | C | D | E
+
+derive instance eqT  :: Eq  T
+derive instance ordT :: Ord T
+
+instance enumT :: Enum T where
+  succ A = Just B
+  succ B = Just C
+  succ C = Just D
+  succ D = Just E
+  succ E = Nothing
+
+  pred A = Nothing
+  pred B = Just A
+  pred C = Just B
+  pred D = Just C
+  pred E = Just D
+
+instance boundedT :: Bounded T where
+  bottom = A
+  top = E
+
+instance boundedEnumT :: BoundedEnum T where
+  cardinality = cardinalityFromRange rangeT
+  toEnum = toEnumFromRange rangeT
+  fromEnum = defaultFromEnum
+
+rangeT :: Range T
+rangeT = range
+
+testRange :: Eff (console :: CONSOLE, assert :: ASSERT) Unit
+testRange = do
+  log "toNonEmptyArray"
+  assert $ toArray (toNonEmptyArray rangeT) == [A, B, C, D, E]
+
+  log "cardinalityFromRange"
+  assert $ cardinality == (Cardinality 5 :: Cardinality T)
+
+  log "toEnumFromRange"
+  assert $ toEnum 0 == Just A
+  assert $ toEnum 1 == Just B
+  assert $ toEnum 2 == Just C
+  assert $ toEnum 3 == Just D
+  assert $ toEnum 4 == Just E