On Mon, May 11, 2009 at 11:32 AM, Sean Devlin <francoisdev...@gmail.com> wrote: > > Here are my thoughts on the three approaches: > > Approach #1: This seems the most straightforward. I'd write a > function that takes a map of conditions, and returns a list of > tuples. You can then do what you want with the list of tuples. > > Approach #2: Remember the first rule of macro club: Don't write > macros if a function will do. From what you've described, this > application wraps a simple SELECT * FROM... , and a macro is overkill.
Yes, you should not write a macro when a function will do, but I think you might be misinterpreting the "spirit" of the rule. Also, the "bottom-up" aspect of programming in Lisp should be kept in mind. In other words, you want to "write a language for solving your problem", and you should definitively use macros for that. So, if a "with-feeds" macro makes sense for the application, do write it! Just make sure the macro is simply syntax sugar for your functions. Following a pattern common in Scheme (at least), the implementation would run along the lines of: (defn call-with-feeds [f] "Call a function with the feeds as an argument" ...) (defmacro with-feeds [feeds & body] `(call-with-feeds (fn [~feeds] ~...@body))) Kind regards, Victor Rodriguez. > Approach #3: This is a good approach once you hit the limits of the > first approach, and before you move on to the second approach. > > I've written SQL apps in Clojure too. And I've used approaches 1 and > 3. I only use approach 2 when I really have to, and I try to have the > macro do as little as possible. > > In summary, try approaches: > > 1 -> 3 -> 2 > > I'll try to throw some code on github this evening so you can see an > example of what I do, and you can decide if it's a good fit for your > application. > > Sean > > On May 11, 4:05 am, Janico Greifenberg <jgre...@googlemail.com> wrote: >> Hi, >> >> I'm writing an RSS-reader using compojure and clojure.contrib.sql. As >> this is my first project in a functional language, I'm not sure about >> how to design the application. The concrete question I'm having right >> now, is how to encapsulate database queries in functions. For my >> RSS-reader, a basic operations is to display lists of feeds that I >> retrieve with the following code: >> >> (sql/with-connection db >> (sql/with-query-results >> feeds >> ["select id, title from feeds order by title"] >> >> As this happens at a few places in the code, I would like to >> encapsulate it somehow. I see several approaches to this, but I'm >> uncertain which of them is the most idiomatic way to do this in >> Clojure. >> >> (1) The straightforward approach seems to be a function that returns >> the feeds. However, I would have to call (doall feeds) to get the data >> out of the internals of contrib.sql/JDBC and into my application. So I >> guess this would not be the most efficient way. >> >> (2) Another idea is to create a function or macro with-feeds that >> wraps the query and creates a binding to be used inside the body. >> >> (3) Or I could have a function that takes another function as a >> parameter which gets called inside with-query-results and gets feeds >> as parameter. >> >> Which of these variants -- or another one that I did not think of -- >> would you recommend? >> >> Janico > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
