Currying

• We can take the definition of fderiv and abstract out the definition of deriv; let's call it g.

    (define (mogrify g f)
      (lambda (x) (g f x)))

    (define (fderiv2 f) (mogrify deriv f))

    (plot (function (fsub (fderiv2 sin) cos) -2pi 2pi))

• In the spirit of the discussion above, the argument f to mogrify is kind of useless. We can hide it inside a new combinator:

    (define (currify g)
      (lambda (f) (lambda (x) (g f x))))

    (define fderiv3 (currify deriv))
    (module+ test
      (for ([x test-points])
        (check-= (cos x) ((fderiv3 sin) x) epsilon)))

• The combinator currify is common enough to be built into the racket library under the name curry

• You can verify that curry is a drop replacement for the function currify; if you read the documentation you can see that it's actually more general.

• for whatever reason curry is not built into plait, but our definition if currify should work fine there.