lambda¶

; f(x,y)=x(1+xy)^2 + y(1−y) + (1+xy)(1−y)
;  => a = 1 + xy
;     b = 1 - y
;  => f(x, y) = xa^2 + yb + ab
(define (f x y)
    (
        (lambda (a b)
            (+ (* x (square a))
               (* y b)
               (* a b)
            )
        )
        (+ 1 (* x y))
        (- 1 y)
    )
)
(f 1 2) ;Value: 4

; Using `let` feature
(define (f x y)
    (let ((a (+ 1 (* x y)))
          (b (- 1 y)))
        (+ (* x (square a))
           (* y b)
           (* a b))))
(f 1 2) ;Value: 4