add demo docs

demo/kitchen-sink/docs/haskell.hs

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+-- Type annotation (optional)
+fib :: Int -> Integer
+ 
+-- With self-referencing data
+fib n = fibs !! n
+        where fibs = 0 : scanl (+) 1 fibs
+        -- 0,1,1,2,3,5,...
+ 
+-- Same, coded directly
+fib n = fibs !! n
+        where fibs = 0 : 1 : next fibs
+              next (a : t@(b:_)) = (a+b) : next t
+ 
+-- Similar idea, using zipWith
+fib n = fibs !! n
+        where fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
+ 
+-- Using a generator function
+fib n = fibs (0,1) !! n
+        where fibs (a,b) = a : fibs (b,a+b)