Add missing instance

lib/Data/Ratio.hs

@@ -17,6 +17,7 @@ import Data.Num
 import Data.Ord
 import Data.Ratio_Type
 import Data.Real
+import Data.RealFrac
 import Text.Show
 
 {- in Data.Ratio_Type
@@ -98,3 +99,16 @@ numerator (x :% _) = x
 
 denominator :: forall a . Ratio a -> a
 denominator (_ :% y) = y
+
+instance (Ord a, Integral a) => RealFrac (Ratio a)  where
+  properFraction (x:%y) = (fromInteger (toInteger q), r:%y)
+    where (q, r) = quotRem x y
+  round r =
+    let
+      (n, f) = properFraction r
+      x = if r < 0 then -1 else 1
+    in  case (compare (abs f) 0.5, odd n) of
+          (LT, _) -> n
+          (EQ, False) -> n
+          (EQ, True) -> n + x
+          (GT, _) -> n + x