Fix fromGFinite for product types

haskell · Jul 1, 2020 · 493f506 · 493f506
1 parent d97cdaf
commit 493f506
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diff --git a/src/System/Random/GFinite.hs b/src/System/Random/GFinite.hs
@@ -171,7 +171,7 @@ instance (GFinite a, GFinite b) => GFinite (a :*: b) where
   {-# INLINE toGFinite #-}
 
   fromGFinite (q :*: r) =
-    toInteger (gcardinality (proxy# :: Proxy# a) * Card (fromGFinite q)) + fromGFinite r
+    toInteger (gcardinality (proxy# :: Proxy# b) * Card (fromGFinite q)) + fromGFinite r
   {-# INLINE fromGFinite #-}
 
 instance Finite Void

diff --git a/src/System/Random/Internal.hs b/src/System/Random/Internal.hs
@@ -603,10 +603,13 @@ class UniformRange a where
   -- >>> import GHC.Generics (Generic)
   -- >>> import Data.Word (Word8)
   -- >>> import System.Random.Stateful
-  -- >>> data Foo = Bar Word8 | Quux Word8 deriving (Show, Generic, Finite, UniformRange)
   -- >>> gen <- newIOGenM (mkStdGen 42)
+  -- >>> data Foo = Bar Word8 | Quux Word8 deriving (Show, Generic, Finite, UniformRange)
   -- >>> Control.Monad.replicateM 10 (uniformRM (Bar 100, Quux 150) gen)
   -- [Bar 148,Bar 251,Bar 195,Quux 115,Quux 52,Bar 123,Bar 239,Bar 195,Quux 150,Quux 31]
+  -- >>> data Tuple = Tuple Bool Word8 deriving (Show, Generic, Finite, UniformRange)
+  -- >>> Control.Monad.replicateM 10 (uniformRM (Tuple False 100, Tuple True 150) gen)
+  -- [Tuple True 141,Tuple True 92,Tuple False 194,Tuple False 191,Tuple True 81,Tuple False 227,Tuple False 166,Tuple False 109,Tuple False 255,Tuple False 222]
   --
   -- @since 1.2.0
   uniformRM :: StatefulGen g m => (a, a) -> g -> m a