Do you want to try for/sum here?
On Oct 14, 2012, at 10:28 PM, Justin R. Slepak wrote: > To use prop:procedure, just give a function which will handle the application > of the structure to some arguments. The define-values is only there because > the for/fold has two accumulators (sum and x) and will therefore return two > values (the values of those accumulators). This means its context has to > expect two values, even though we don't really care about the second value. > The x* is just a name. > > --- > Justin Slepak > PhD student, Computer Science dept. > > ----- Original Message ----- > From: Gregory Woodhouse <gregwoodho...@me.com> > To: Justin R. Slepak <jrsle...@ccs.neu.edu> > Sent: Sun, 14 Oct 2012 22:07:59 -0400 (EDT) > Subject: Re: [racket] Function composition in Racket > > Thanks! This does what I want. To tell you the truth, I've shied away from > prop:procedure (probably more due to my own confusion than anything else!). > The define-values here seems a bit mysterious, but I assume the point is to > support the recursive polynomial evaluation function? Is x* a special syntax > here or just a name. I see sum in both for/fold and values, but the x* in > define-values is mysterious. > > On Oct 14, 2012, at 4:57 PM, "Justin R. Slepak" <jrsle...@ccs.neu.edu> wrote: > >> Instead of trying to peek inside a lambda, you could implement polynomials >> as (transparent) structs and use prop:procedure to allow them to be applied >> to numbers: >> >> (struct polynomial (coeffs) >> #:transparent >> #:property prop:procedure >> (lambda (poly num) >> (define-values (result x*) >> (for/fold ([sum 0] >> [x 1]) >> ([c (polynomial-coeffs poly)]) >> (values (+ sum (* c x)) >> (* x num)))) >> result)) >> >> This would let you implement functions that crunch on polynomials. As for >> using existing operators' names, maybe generics can get you that? >> >> --- >> Justin Slepak >> PhD student, Computer Science dept. > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
