Aaah, man. Thanks. Shutdown the pc for the night so u will try tomorrow. On May 2, 2013 10:35 PM, "Jay McCarthy" <jay.mccar...@gmail.com> wrote:
> You were close to what you want. Here's a version with a nice utility > and then the underlying machinery that makes it: > > #lang racket > (require (for-syntax racket/syntax)) > > (define-syntax (double-define stx) > (syntax-case stx (double-define) > [(_ id val1 val2) > (with-syntax ([id-1 (format-id #'id "~a-1" #'id)] > [id-2 (datum->syntax > #'id > (string->symbol > (format "~a-2" > (syntax->datum > #'id))))]) > #'(begin (define id-1 val1) > (define id-2 val2)))])) > > (double-define id 3 7) > (displayln id-1) > (displayln id-2) > > On Thu, May 2, 2013 at 8:29 PM, Sean McBeth <sean.mcb...@gmail.com> wrote: > > Hi there! > > > > I'm pretty new to Racket, though not the basic concepts of functional > > programming [1] Maybe I don't need macros here at all, but it seemed like > > the right sort of lever when I first started, but now I'm pretty stuck[2] > > and I don't understand enough about the macro system yet to be able to > > figure this out. > > > > Basically, I'm trying to make a database migration tool + relational > mapper. > > I'd like to be able to define my tables in an abbreviated Racket syntax > and > > use the definition to generate everything from the create-table SQL > scripts, > > a few, basic CRUD-scripts-for-all-columns to structs that will mirror a > full > > table row when processing the query results. > > > > Right now, the table definition looks like this: > > > > (define-table tickets get-all-tickets > > ([ticket_id serial primary-key] > > [priority int nullable] ;; I believe in making not-null the default > case > > [description (varchar max)] > > [finished_on datetime (default "9999-12-31 23:59:59.999")]) > > > > And this is pretty easy to parse into some "table" structs that describe > > everything fairly sufficiently[3]: > > https://gist.github.com/capnmidnight/5506674 > > > > Now, my sticking point is that I don't want to have explicitly define > that > > "get-all-tickets" identifier. I notice that, in my creating the "column" > > struct, I've received a number of procedures for the constructor and > field > > accessors, all given a prefix of "column" for their identifier. So at > first > > glance, it seems like there are forms like struct that are capable of > > dynamically defining identifiers. > > > > So, I stepped into the definition for struct and tried to make sense of > it, > > but the best I could figure out was that struct used syntax-case instead > of > > syntax-rules. It was a bit of a hair-ball for me, I couldn't suss out the > > cross references, and at least at this late of an hour I'm having trouble > > understanding the documentation on syntax-case. > > > > Specifically, I tried to do something like: > > > > (define-syntax (double-define stx) > > (syntax-case stx (double-define) > > [(_ id val1 val2) > > #`(begin (define id-1 val1) > > (define id-2 val2))])) > > > > (double-define id 3 7) > > (displayln id-1) ;; error "id-1 unbound identifier" > > (displayln id-2) > > > > I then tried something like: > > > > (define-syntax (double-define stx) > > (syntax-case stx (double-define) > > [(_ id val1 val2) > > (with-syntax ([id-1 #'(string->symbol (format "~a-1" id))] ;; error > > "define: not an identifier, identifier with default, or keyword for > > procedure argument" > > [id-2 #'(string->symbol (format "~a-2" id))]) > > #'(begin (define id-1 val1) > > (define id-2 val2)))])) > > > > (double-define id 3 7) > > (displayln id-1) > > (displayln id-2) > > > > Clearly, not correct. > > > > I could make the table struct into a table class and then just define a > > get-all method that does what I want, but that kind of feels like giving > up > > and I'm more interested in using this to learn more about using macros, > as > > it has already done for me. > > > > > > > > [1] Functional C# is something of a job safety program of mine :P > > > > [2] i.e. been banging my head against the desk for the last 6 hours. I > have > > gotten pretty comfortable with syntax-rules though, so it wasn't a > complete > > waste. > > > > [3] This isn't the final form, but I'm just pushing some code around to > try > > to get the basic concepts working. For example, the get-all-tickets > > procedure wouldn't just return the query, it'd eventually execute it and > > return the results. > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > > > -- > Jay McCarthy <j...@cs.byu.edu> > Assistant Professor / Brigham Young University > http://faculty.cs.byu.edu/~jay > > "The glory of God is Intelligence" - D&C 93 >
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