[racket] Macros and dynamically generating identifiers

Aaah, man. Thanks. Shutdown the pc for the night so u will try tomorrow.
On May 2, 2013 10:35 PM, "Jay McCarthy" <jay.mccarthy at 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.mcbeth at 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 <jay at cs.byu.edu>
> Assistant Professor / Brigham Young University
> http://faculty.cs.byu.edu/~jay
>
> "The glory of God is Intelligence" - D&C 93
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20130502/6272017b/attachment.html>