--
-- script:  tail.es
--
-- created: 14/8/97 by Andrew Rock
--
-- purpose: experiments with tail recursion.
--

print_mode = f 

-- fact :: Int -> Int
--
-- fact n returns n!
--
-- linear recursive implementation
--
fact n = if n == 0
            then 1
            else n * fact (n-1)
		
		
-- fact' :: Int -> Int
--
-- fact' n returns n!
--
-- tail recursive implementation
--
fact' n = fact'' n 1
fact'' n p = if n == 0
                then p
	        else fact'' (n-1) (p * n)


-- fib :: Int -> Int
--
-- fib n returns the n'th Fibonacci number in the sequence 0, 1, 1, 2, 3, ...
--
-- tree recursive implementation
--
fib n = if n == 0
           then 0
	   else if n == 1
	           then 1
	           else fib (n-1) + fib (n-2)


-- fib' :: Int -> Int
-- 
-- fib' n returns the n'th Fibonacci number in the sequence 0, 1, 1, 2, 3, ...
--
-- tail recursive implementation
--
fib' n = fib'' n 0 1
fib'' n a b = if n == 0
                 then a
		 else fib'' (n-1) b (a+b)