<div dir="ltr">Wow, section 4 is exactly, almost word for word, what I was trying to do. This is a great resource. </div><div class="gmail_extra"> <div class="gmail_quote">On Fri, May 3, 2013 at 7:35 AM, Philipp Dikmann <<a href="mailto:philipp@dikmann.de" target="_blank">philipp@dikmann.de</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div bgcolor="#FFFFFF" text="#000000"> You might have already read it, but I also found the guide "Fear of Macros" by Greg Hendershott incredibly helpful in understanding them, especially considering things like with-syntax and format-id: <a href="http://www.greghendershott.com/fear-of-macros/index.html" target="_blank">http://www.greghendershott.com/fear-of-macros/index.html</a><div><div class="h5"> <div>On 03.05.13 04:57, Sean McBeth wrote: </div> <blockquote type="cite"> I think I get it just from reading it (in bed, on the phone, annoying the wife). I had tried to do almost this very thing with datum->syntax at one point, but I had put the quotesyntax on datum->syntax, not on id directly. I don't understand why that would make a difference, it seems like it is similar to doing (list 'a 'b) instead of '(a b)... oh, nope, now I get it. It specifically *is* similar, except my second example should have been '(list a b). <div class="gmail_quote">On May 2, 2013 10:38 PM, "Sean McBeth" <<a href="mailto:sean.mcbeth@gmail.com" target="_blank">sean.mcbeth@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Aaah, man. Thanks. Shutdown the pc for the night so u will try tomorrow. <div class="gmail_quote">On May 2, 2013 10:35 PM, "Jay McCarthy" <<a href="mailto:jay.mccarthy@gmail.com" target="_blank">jay.mccarthy@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> 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 <<a href="mailto:sean.mcbeth@gmail.com" target="_blank">sean.mcbeth@gmail.com</a>> 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]: > <a href="https://gist.github.com/capnmidnight/5506674" target="_blank">https://gist.github.com/capnmidnight/5506674</a> > > 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: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > -- Jay McCarthy <<a href="mailto:jay@cs.byu.edu" target="_blank">jay@cs.byu.edu</a>> Assistant Professor / Brigham Young University <a href="http://faculty.cs.byu.edu/%7Ejay" target="_blank">http://faculty.cs.byu.edu/~jay</a> "The glory of God is Intelligence" - D&C 93 </blockquote> </div> </blockquote> </div> <fieldset></fieldset> <pre>____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </pre> </blockquote> </div></div></div> </blockquote></div> </div>