add Random tuple instances

closes haskell#26

System/Random.hs

@@ -448,6 +448,46 @@ instance Random CDouble where
   -- random rng = case random rng of
   --             (x,rng') -> (realToFrac (x::Double), rng')
 
+instance (Random a, Random b) => Random (a,b) where
+  randomR ((lox,loy),(hix,hiy)) rng = let (x,rng')  = randomR (lox,hix) rng
+                                          (y,rng'') = randomR (loy,hiy) rng'
+                                       in ((x,y),rng'')
+  random rng = let (x,rng')  = random rng
+                   (y,rng'') = random rng'
+                in ((x,y),rng'')
+
+instance (Random a, Random b, Random c) => Random (a,b,c) where
+  randomR ((lx,ly,lz),(hx,hy,hz)) rng =
+    case randomR (((lx,ly),lz),((hx,hy),hz)) rng of
+      (((x,y),z),rng') -> ((x,y,z),rng')
+  random rng =
+    case random rng of
+      (((x,y),z),rng') -> ((x,y,z),rng')
+
+instance (Random a, Random b, Random c, Random d) => Random (a,b,c,d) where
+  randomR ((lx,ly,lz,lw),(hx,hy,hz,hw)) rng =
+    case randomR (((lx,ly),lz,lw),((hx,hy),hz,hw)) rng of
+      (((x,y),z,w),rng') -> ((x,y,z,w),rng')
+  random rng =
+    case random rng of
+      (((x,y),z,w),rng') -> ((x,y,z,w),rng')
+
+instance (Random a, Random b, Random c, Random d, Random e) => Random (a,b,c,d,e) where
+  randomR ((lx,ly,lz,lw,lv),(hx,hy,hz,hw,hv)) rng =
+    case randomR (((lx,ly),lz,lw,lv),((hx,hy),hz,hw,hv)) rng of
+      (((x,y),z,w,v),rng') -> ((x,y,z,w,v),rng')
+  random rng =
+    case random rng of
+      (((x,y),z,w,v),rng') -> ((x,y,z,w,v),rng')
+
+instance (Random a, Random b, Random c, Random d, Random e, Random f) => Random (a,b,c,d,e,f) where
+  randomR ((lx,ly,lz,lw,lv,lu),(hx,hy,hz,hw,hv,hu)) rng =
+    case randomR (((lx,ly),lz,lw,lv,lu),((hx,hy),hz,hw,hv,hu)) rng of
+      (((x,y),z,w,v,u),rng') -> ((x,y,z,w,v,u),rng')
+  random rng =
+    case random rng of
+      (((x,y),z,w,v,u),rng') -> ((x,y,z,w,v,u),rng')
+
 mkStdRNG :: Integer -> IO StdGen
 mkStdRNG o = do
     ct          <- getCPUTime