Merge pull request #12 from anttih/gcd-ratio

Define gcd for Ratio

Author: anttih

src/Data/Ratio.purs

@@ -1,4 +1,9 @@
-module Data.Ratio where
+module Data.Ratio
+  ( Ratio(Ratio)
+  , numerator
+  , denominator
+  , gcd
+  ) where
 
 import Prelude
 
@@ -27,3 +32,9 @@ numerator (Ratio a _) = a
 
 denominator :: forall a. Ratio a -> a
 denominator (Ratio _ b) = b
+
+gcd :: forall a. (Eq a, EuclideanRing a) => Ratio a -> a
+gcd (Ratio m n)
+  | n == zero = m
+  | otherwise = gcd (Ratio n (m `mod` n))
+

src/Data/Rational.purs

@@ -8,7 +8,7 @@ module Data.Rational
 
 import Prelude
 import Data.Int as Int
-import Data.Ratio (Ratio(Ratio))
+import Data.Ratio (Ratio(Ratio), gcd)
 
 newtype Rational = Rational (Ratio Int)
 
@@ -55,16 +55,11 @@ fromInt :: Int -> Rational
 fromInt i = Rational $ Ratio i 1
 
 reduce :: Rational -> Rational
-reduce (Rational (Ratio a b)) =
-  let x = a / gcd a b
-      y = b / gcd a b
+reduce (Rational ratio@(Ratio a b)) =
+  let x = a / gcd ratio
+      y = b / gcd ratio
   in Rational $ Ratio (x * signum y) (abs y)
 
-gcd :: Int -> Int -> Int
-gcd m n
-  | n == 0 = m
-  | otherwise = gcd n (m `mod` n)
-
 signum :: Int -> Int
 signum 0 = 0
 signum x' | x' < 0 = -1