On Sun, Feb 16, 2014 at 08:19:48PM -0600, David Novogrodsky wrote: > All, > > First here is the code I entered in the interaction window. The question I > have are about these lines: > > (require xml net/url) > > (define u (string->url "http://localhost:8080/foo/testing";)) > > (url-path u) > '(#<path/param> #<path/param>) > > (map path/param-path (url-path u)) > '("foo" "testing”) > > I took an online course on Systematic Programming and it used Racket for its > examples. Well, actually it used the intermediate learning language for the > class. now I am trying to learn Racket.
I had almost finished this response when I saw Professor Felleisen had already responded. Some of this is therefore redundant, but perhaps it is useful for some additional context. > The questions: > 1. Take a look at the fourth line. What is this called? Is this a list of > references or pointers? It's a list of path/param objects. I suspect you are thrown by the funny-looking #<path/param> parts. That is how opaque struct instances are printed. Structure printing is documented here: http://doc.racket-lang.org/reference/printing.html#%28part._print-structure%29 but that has much more detail than you need right now, and very little that applies to this example anyway. > 2. I am trying to find if help-desk information about path/param-path > function, but I have not been able to find any. When I search for `path/param-path' online I get: http://doc.racket-lang.org/search/index.html?q=path/param-path which links to the docs for `path/param': http://doc.racket-lang.org/net/url.html?q=path/param-path#%28def._%28%28lib._net%2Furl-structs..rkt%29._path%2Fparam-path%29%29 In case you aren't aware, a structure type `foo' with a field `bar' will typically have an accessor function `foo-bar' which takes a foo instance and returns the value of its bar field. In this case, `path/param-path' is the accessor function for the `path' field of a `path/param' object. > This function returns returns the resolved parts of the path of a URL. > What is the proper term for taking the list in line four and returning > the list in line five? I'm not sure what you are looking for here -- a word that means "using `map'"? I'm not a computer scientist, but maybe "mapping" or "transforming"? Perhaps you are referring to the fact that path/param objects are wrappers or decorators around simple strings, so your map operation is "unwrapping" or "deconstructing"? > 3. What is the proper term for what the function url-path returns? A search for `url-path' brings me to: http://doc.racket-lang.org/net/url.html?q=url-path#%28def._%28%28lib._net%2Furl-structs..rkt%29._url-path%29%29 which shows that the `path' field of a `url' object is a: (listof path/param?) In other words, `url-path' will return a list of `path/param' objects. > 4. Does anyone have an example of using the results from line 4 as part of a > check-expect test? (check-expect (map path/param-path (url-path u)) (list "foo" "testing")) I initially had trouble using check-expect directly with the result of url-path, I think because of the problem described here: http://www.mail-archive.com/users@racket-lang.org/msg09011.html If you want to learn Racket, you might want to switch the language (control-L in DrRacket) to Racket, and use rackunit for unit testing: #lang racket (require net/url) (require rackunit) (define u (string->url "http://localhost:8080/foo/testing";)) (check-equal? (map path/param-path (url-path u)) (list "foo" "testing")) David ____________________ Racket Users list: http://lists.racket-lang.org/users
