Merge pull request #3 from purescript/lazy

Add Lazy instances

Author: paf31

bower.json

@@ -18,7 +18,8 @@
     "package.json"
   ],
   "dependencies": {
-    "purescript-arrays": "*",
-    "purescript-monoid": "*"
+    "purescript-arrays": "~0.2.0",
+    "purescript-monoid": "*",
+    "purescript-control": "~0.2.0"
   }
 }

src/Data/Tuple.purs

@@ -2,6 +2,7 @@ module Data.Tuple where
 
 import Data.Array
 import Data.Monoid
+import Control.Lazy
 
 data Tuple a b = Tuple a b
 
@@ -27,11 +28,20 @@ instance applicativeTuple :: (Monoid a) => Applicative (Tuple a) where
   pure = Tuple mempty
 
 instance bindTuple :: (Semigroup a) => Bind (Tuple a) where
-  (>>=) (Tuple a1 b) f = case f b of 
+  (>>=) (Tuple a1 b) f = case f b of
     Tuple a2 c -> Tuple (a1 <> a2) c
 
 instance monadTuple :: (Monoid a) => Monad (Tuple a)
 
+instance lazyTuple :: (Lazy a, Lazy b) => Lazy (Tuple a b) where
+  defer f = Tuple (defer $ \_ -> fst (f unit)) (defer $ \_ -> snd (f unit))
+
+instance lazyLazy1Tuple :: (Lazy1 l1, Lazy1 l2) => Lazy (Tuple (l1 a) (l2 b)) where
+  defer f = Tuple (defer1 $ \_ -> fst (f unit)) (defer1 $ \_ -> snd (f unit))
+
+instance lazyLazy2Tuple :: (Lazy2 l1, Lazy2 l2) => Lazy (Tuple (l1 a b) (l2 c d)) where
+  defer f = Tuple (defer2 $ \_ -> fst (f unit)) (defer2 $ \_ -> snd (f unit))
+
 fst :: forall a b. Tuple a b -> a
 fst (Tuple a _) = a