Data commit

Task/Null-object/Haskell/null-object-1.hs

@@ -0,0 +1,3 @@
+undefined      -- undefined value provided by the standard library
+error "oops"   -- another undefined value
+head []        -- undefined, you can't take the head of an empty list

Task/Null-object/Haskell/null-object-2.hs

@@ -0,0 +1 @@
+ data Maybe a = Nothing | Just a

Task/Null-object/Haskell/null-object-3.hs

@@ -0,0 +1,3 @@
+case thing of
+ Nothing -> "It's Nothing. Or null, whatever."
+ Just v  -> "It's not Nothing; it is " ++ show v ++ "."

Task/Null-object/Haskell/null-object-4.hs

@@ -0,0 +1,4 @@
+add_two_maybe_numbers x y do
+  a <- x
+  b <- y
+  return (a+b)

Task/Null-object/Haskell/null-object-5.hs

@@ -0,0 +1,4 @@
+*Main> add_two_maybe_numbers (Just 2) (Just 3)
+Just 5
+*Main> add_two_maybe_numbers (Just 2) Nothing
+Nothing