feat: add Random instance

Closes #18.

Author: pbrisbin

closed.cabal

@@ -39,6 +39,7 @@ library
     , deepseq
     , hashable
     , persistent
+    , random
     , text
   default-language: Haskell2010
 

library/Closed/Internal.hs

@@ -32,6 +32,7 @@ import Database.Persist.Sql
 import GHC.Generics
 import GHC.Stack
 import GHC.TypeLits
+import System.Random (Random (..))
 import Test.QuickCheck
 import Text.ParserCombinators.ReadP (pfail, readP_to_S, readS_to_P)
 
@@ -164,6 +165,12 @@ instance (KnownNat a, KnownNat b, a <= b) => Integral (Closed a b) where
 
 instance NFData (Closed a b)
 
+instance (KnownNat a, KnownNat b, a <= b) => Random (Closed a b) where
+  randomR (a, b) g =
+    let (x, g') = randomR (getClosed a, getClosed b) g
+    in  (unsafeClosed x, g')
+  random = randomR (minBound, maxBound)
+
 instance Hashable (Closed a b)
 
 instance ToJSON (Closed a b) where

package.yaml

@@ -21,6 +21,7 @@ library:
   dependencies:
     - deepseq
     - hashable
+    - random
     - QuickCheck
 
 tests: