Add Uniform instance for Maybe and Either

haskell · Oct 27, 2024 · 6fcb4f5 · 6fcb4f5
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # 1.3.0
 
+* Add `Uniform` instance for `Maybe` and `Either`
 * Add `SplitGen` and `splitGen`
 * Add `shuffleList` and `shuffleListM`: [#140](https://github.com/haskell/random/pull/140)
 * Add `mkStdGen64`: [#155](https://github.com/haskell/random/pull/155)

diff --git a/src/System/Random/Internal.hs b/src/System/Random/Internal.hs
@@ -109,7 +109,7 @@ import GHC.ST (ST(..))
 import GHC.Word
 import Numeric.Natural (Natural)
 import System.IO.Unsafe (unsafePerformIO)
-import System.Random.GFinite (Cardinality(..), GFinite(..))
+import System.Random.GFinite (Cardinality(..), GFinite(..), Finite)
 import qualified System.Random.SplitMix as SM
 import qualified System.Random.SplitMix32 as SM32
 import Data.Kind
@@ -1474,6 +1474,10 @@ instance UniformRange Bool where
   {-# INLINE uniformRM #-}
   isInRange = isInRangeOrd
 
+instance (Finite a, Uniform a) => Uniform (Maybe a)
+
+instance (Finite a, Uniform a, Finite b, Uniform b) => Uniform (Either a b)
+
 -- | See [Floating point number caveats](System-Random-Stateful.html#fpcaveats).
 instance UniformRange Double where
   uniformRM (l, h) g