You can have unresolved symbols within a macro with: ~'symbol David
On Wed, Dec 17, 2008 at 3:30 AM, Meikel Brandmeyer <m...@kotka.de> wrote: > > Hi, > > I'd like to propose/put up for discussion a change to the unquote > handling. > I basically ran into the following problem: > > I'd like to embed a DSL into my system. Using macros it should be > possible > to define a language, which looks like usual Clojure. Simply quote the > form > and pass it to a function, which knows how to handle the commands. > > However I hit a roadblock. Coming from Scheme, I tried the following > approach. > > A hypothetical SQL embedding: > > (def x 5) > (sql col1 from table1 where col2 = ~x) > > Or a hypothetical cljsh (inspired by scsh): > > (def *cmd* "/usr/bin/command") > (run (~*cmd* -option 1 -another argument foo bar)) > > In Scheme this is done, by quoting the macros argument using the > quasiquote form. In Clojure, however, this style is not possible since > we are > missing quasiquote. Here a short list of examples on how the different > quotations work: > > (quote (foo ~x bar)) > => Failure in Clojure. > => In some Schemes: (foo (unquote x) bar), where , (aka. ~) translates > to some unquote form. It just quotes everything. Also the unquote. > > (quasiquote (foo ~x bar)) > => Not available in Clojure. > => (foo 5 bar) in Scheme > > (syntax-quote (foo ~x bar)) > => (assuming ` would have a syntax-quote form as ' does with quote) > (my.ns/foo 5 maybe.some.other.ns/bar) > => Not available in Scheme, AFAIK. > > So as you see, the above style is not possible, since in Clojure you > only > have the choice to be static or resolve all the symbols. If I want to > use > the style anyway, I have to jump through hoops and rewrite the quoted > form in my handler function, be it replacing somehow marked or named > symbols with values from the environment or be it renormalising all > the > symbols. (But what if the user injected a qualified symbol with ~?) > > So I came to the question of whether it is possible to include a > similar > quasiquote form, which does not resolve the symbols inside? It would > be a philosophy of "Unquote, what the user wants to be unquoted, and > leave the rest to me. I know how to handle it." > > And when were are at it: maybe also provide a syntax-quote, unquote > and unquote-splice forms? > > Finally, I skipped the obvious question: Does this make sense at all? > I like this way of including a sub-language. However, is it > "idiomatic"? > (for some definition of "idiomatic") > > Maybe there is already a different solution, which I just don't see at > the moment. > > Sincerely > Meikel > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
