; Continuation Passing Style Demo

;;;; From http://en.wikibooks.org/wiki/Haskell/Continuation_passing_style
;;;;    
;;;;  Example: A simple module, no continuations
;;;;    
;;;;    -- We assume some primitives add and square for the example:
;;;;    
;;;;    add :: Int -> Int -> Int
;;;;    add x y = x + y
;;;;    
;;;;    square :: Int -> Int
;;;;    square x = x * x
;;;;    
;;;;    pythagoras :: Int -> Int -> Int
;;;;    pythagoras x y = add (square x) (square y)
;;;;    
;;;;  And the same function pythagoras, written in CPS looks like this:
;;;;    
;;;;  Example: A simple module, using continuations
;;;;    
;;;;    -- We assume CPS versions of the add and square primitives,
;;;;    -- (note: the actual definitions of add'cps and square'cps are not
;;;;    -- in CPS form, they just have the correct type)
;;;;    
;;;;    add'cps :: Int -> Int -> (Int -> r) -> r
;;;;    add'cps x y k = k (add x y)
;;;;    
;;;;    square'cps :: Int -> (Int -> r) -> r
;;;;    square'cps x k = k (square x)
;;;;    
;;;;    pythagoras'cps :: Int -> Int -> (Int -> r) -> r
;;;;    pythagoras'cps x y k =
;;;;     square'cps x $ \x'squared ->
;;;;      square'cps y $ \y'squared ->
;;;;       add'cps x'squared y'squared $ \sum'of'squares ->
;;;;        k sum'of'squares


(define (cps'add x y r) (r (+ x y)))

(define (cps'square x r) (r (* x x)))

(define (cps'pythag x y r)
        (cps'square x
             (lambda (xx) (cps'square y
                               (lambda (yy) (cps'add xx yy
                                                 (lambda (zz) (r zz))))))))

(say '(cps'pythag 3 4 --->))
(cps'pythag 3 4 (lambda (x) (assert-equal 'XXV. (say (roman x)))))