From 99f9d18ee8c8f7dd52152601781415af3ae59bbe Mon Sep 17 00:00:00 2001
From: Matthew Leon <ml@matthewleon.com>
Date: Mon, 6 Mar 2017 17:02:20 +0000
Subject: [PATCH] enum gen

A handy generator for types that implement the BoundedEnum class.
---
 bower.json                   |  4 +++-
 src/Test/QuickCheck/Gen.purs | 14 +++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/bower.json b/bower.json
index 73ab358..0e8c915 100644
--- a/bower.json
+++ b/bower.json
@@ -27,6 +27,8 @@
     "purescript-lists": "^3.0.0",
     "purescript-random": "^2.0.0",
     "purescript-strings": "^2.0.0",
-    "purescript-transformers": "^2.0.0"
+    "purescript-transformers": "^2.0.0",
+    "purescript-enums": "^2.0.1",
+    "purescript-partial": "^1.2.0"
   }
 }
diff --git a/src/Test/QuickCheck/Gen.purs b/src/Test/QuickCheck/Gen.purs
index d976f85..7beca14 100644
--- a/src/Test/QuickCheck/Gen.purs
+++ b/src/Test/QuickCheck/Gen.purs
@@ -39,14 +39,17 @@ import Control.Monad.State (State, runState, evalState)
 import Control.Monad.State.Class (state, modify)
 
 import Data.Array ((!!), length)
+import Data.Enum (class BoundedEnum, fromEnum, toEnum)
 import Data.Foldable (fold)
 import Data.Int (toNumber)
 import Data.List (List(..), toUnfoldable)
-import Data.Maybe (fromMaybe)
+import Data.Maybe (fromMaybe, fromJust)
 import Data.Monoid.Additive (Additive(..))
 import Data.Newtype (unwrap)
 import Data.Tuple (Tuple(..), fst, snd)
 
+import Partial.Unsafe (unsafePartial)
+
 import Math as M
 
 import Test.QuickCheck.LCG (Seed, lcgPerturb, lcgN, lcgNext, runSeed, randomSeed)
@@ -155,6 +158,15 @@ arrayOf1 g = sized $ \n ->
      xs <- vectorOf (k - one) g
      pure $ Tuple x xs
 
+-- | Create a random generator for a finite enumeration.
+-- | `toEnum i` must be well-behaved:
+-- | It must return a value wrapped in Just for all Ints between
+-- | `fromEnum bottom` and `fromEnum top`.
+enum :: forall a. BoundedEnum a => Gen a
+enum = do
+  i <- chooseInt (fromEnum (bottom :: a)) (fromEnum (top :: a))
+  pure (unsafePartial $ fromJust $ toEnum i)
+
 replicateMRec :: forall m a. MonadRec m => Int -> m a -> m (List a)
 replicateMRec k _ | k <= 0 = pure Nil
 replicateMRec k gen = tailRecM go (Tuple Nil k)