On Thu, Jul 6, 2017 at 8:53 AM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu> wrote:
> Just for clarity, here's an example using `set!` and `define`, > although I wouldn't really suggest this style: > > #lang typed/racket > > (: f : Real -> Real) > (define (f x) > (define rand-value (random)) > (define new-value (+ x rand-value)) > (set! new-value (- new-value x)) > new-value) > > Sam > You wouldn't suggest it because of the set! or because of the defines? define seems like a useful construct -- if you're already inside the desired scope then (define x ...) is a less verbose syntax than (let ((x ...)) ...) and it doesn't introduce another layer of indentation. > > On Wed, Jul 5, 2017 at 10:52 PM, Alasdair McAndrew <amc...@gmail.com> > wrote: > > Well, after a bit of fiddling, I've discovered I can indeed do what I > need to, with a judicious use of "let" for creating a swag of random > values, and ensuring that their use is all within the scope of let. So > far, all good! > > > > On Thursday, 6 July 2017 10:54:53 UTC+10, Royall Spence wrote: > >> Sounds like two questions wrapped into one. When it comes to setting > >> names to values, Scheme programming encourages the use of a "let" > >> expression to bind values to names inside of a (usually narrow) scope > >> rather than assigning a value to a variable. See more here: > >> https://docs.racket-lang.org/guide/let.html > >> > >> As for the typed random value, the Flonum from (random) should be fine > >> since a Flonum is also a Real. Can you provide a short example of > >> runnable code that exposes the problem you're having? > >> > >> On Wed, Jul 5, 2017, at 08:39 PM, Alasdair McAndrew wrote: > >> > I'm doing a little programming which requires the use of some random > >> > numbers. Basically I add a random value at one stage, and subtract > it a > >> > bit later. Something like this pseudo-code (where "x" is an existing > >> > variable): > >> > > >> > set rand_value <- (random) > >> > set new_value <- x + rand_value > >> > > >> > ... do stuff ... > >> > > >> > set new_value <- new_value - rand_value > >> > > >> > All values may be considered Reals. I tried to do this in Typed > Racket, > >> > where x was of type "Real" and got errors about mismatched types: > >> > "(random)" produces a "flonum". I was also using "set!" for the > >> > assignment of the random value, which I understand to be poor > practice: > >> > how would I do something like the above in a more "rackety" manner? > >> > Thank you! > >> > > >> > -- > >> > You received this message because you are subscribed to the Google > Groups > >> > "Racket Users" group. > >> > To unsubscribe from this group and stop receiving emails from it, > send an > >> > email to racket-users+unsubscr...@googlegroups.com. > >> > For more options, visit https://groups.google.com/d/optout. > > > > -- > > You received this message because you are subscribed to the Google > Groups "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
