Also, check out the net/head library: http://docs.racket-lang.org/net/head.html?q=header%20parse&q=header
Robby On Thu, Jul 18, 2013 at 2:25 AM, Carl Eastlund <c...@ccs.neu.edu> wrote: > Chris, > > The regexp-match* function has a rather complex input/output > specification, because it is doing a lot of things at once. If you only > want the first match of a regular expression, you might want to consider > regexp-match instead (no *); its specification is slightly simpler, though > still a little complex. > > The car function, on the other hand, is very straightforward. Given a > list, it extracts and returns the first element of that list. The name > "car" is rather anachronistic; Racket also has a function called first that > does the same thing. If it makes things clearer to you, use that one > instead. > > If using functions like regexp-match* and car is giving you trouble in > your program, I suggest playing around with them in racket or DrRacket, > outside of any program. Just apply regexp-match*, car, and any other > functions you want to learn more about, to different inputs and see what > results you get. That should give you a clearer idea of how to put them > together in your program. It will also give you a starting point for > asking more concrete questions about specific inputs and outputs the rest > of us can look at, try ourselves, and explain. > > For instance, see what (regexp-match* "[abc]+" "banana") produces. Also > see what (car (list 1 2 3)) produces. Try string->list and list->string if > you're curious to see how they work, too. > > When you've got a handle on how each function works individually, you can > get back to your program. Write lots of tests for your program, and break > your program up into smaller "helper" functions, and write tests for them > too. All these steps will make it much easier to see what each function is > doing, and if the output isn't what you expected it to be, these steps will > help you figure out where things went wrong and why. > > Thanks for your question, feel free to ask more if you have them. Good > luck! > > Carl Eastlund > > P.S. I know this isn't a simple "regexp-match* works like this" answer. > Your question is actually several questions -- what kind of output does > regexp-match* produce, how does one convert between lists and strings, how > does the function car work, and so forth. I hope the process above will > help you work through some of the complexity and get to some simpler, more > direct questions that are easier to tackle. Sorry if this feels like a bit > of a runaround, but I think you'll get a handle on it pretty quick! > > On Thu, Jul 18, 2013 at 2:29 AM, <m0nas...@tengulabs.com> wrote: > >> Hi, I'm super new to Racket, but had what I hope isn't too >> embarrassingly easy of a question. >> >> I'm writing a program that parses SMTP headers in order to automate some >> business-y workflow. I managed to put together a series of >> "regexp-match*"s to parse out the specific identifiers I was looking for >> (although truth be told, mail headers are surprisingly nonstandard even >> within a single message), and ran into an error later when trying to >> string-append them. I eventually discovered by process of elimination >> (after trying string?, etc. to figure out how the results of a regexp >> are stored) that they were a list. I tried list->string and a few other >> methods to covert them, but wasn't having any luck. >> >> I eventually discovered that I could sort of cheat, by just wrapping the >> regexp-match function with a car (which worked, because this particular >> list only had one element), and then it was usable from then on (and >> validated true from "string?"). >> >> So, my actual question is two-fold. First, It seems like I must have >> missed some pretty obvious way to capture the initial regex match as a >> string, but I'm not sure what it was. >> >> And secondly, and actually what I'm more curious about, why does it >> become a string when wrapped by car? I would have presumed that car >> would leave structures as a list. >> >> Again, I apologize if this is something dead-simple, but I really did >> spend a good portion of the day stuck in "regex-hell", and so was >> curious. >> >> -Chris >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> >> > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > >
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