Add genBoundedEnum (#29)

* Add `genBoundedEnum`

* Use `enumFromTo` for `genBoundedEnum`

* Un-bias the enum generator

Author: garyb

src/Data/Enum/Gen.purs

@@ -0,0 +1,18 @@
+module Data.Enum.Gen where
+
+import Prelude
+
+import Control.Monad.Gen (class MonadGen, elements)
+import Data.Enum (class BoundedEnum, succ, enumFromTo)
+import Data.Maybe (Maybe(..))
+import Data.NonEmpty ((:|))
+
+-- | Create a random generator for a finite enumeration.
+genBoundedEnum :: forall m a. MonadGen m => BoundedEnum a => m a
+genBoundedEnum =
+  case succ bottom of
+    Just a →
+      let possibilities = enumFromTo a top :: Array a
+      in elements (bottom :| possibilities)
+    Nothing →
+      pure bottom