On Tue, 7 Dec 2010 02:58:11 -0500 Ken Wesson <kwess...@gmail.com> wrote:
> On Tue, Dec 7, 2010 at 2:15 AM, javajosh <javaj...@gmail.com> wrote: > > Mike and I have had a nice off-line conversation where we enumerated > > the possible things that can come after open-parens. I listed 7, he > > added 3: That wasn't meant to be offline, but it's probably not worth resending. However... > >> 1. A value (if the paren has a tick '( ) > >> 2. A function. > >> 3. A map - which is a psuedo function that takes a key as an arg. > >> 4. A keyword - which is a psuedo function that takes a map as an arg. > >> 5. A macro. This is the normal case, I think. Looking through the mailing > >> list, it appears that most clojure programming questions revolve around > >> which one of the hundreds of macros to invoke and in which order! > >> 6. The Java form: (MyClass. ) > >> 7. The java method form (.doSomething) > > 8. A function returning a function to invoke - ((find-my-function) ) > > 9. A loop - (recur ) > > 10. The anonymous function macro: #( ) > > > > So, at least I know why I feel uneasy about open paren! It's super > > overloaded. > > Not really. (...) is a non-atomic s-expression. If it's evaluated > unquoted, the first nested s-expression is evaluated and if it's not > callable an exception is thrown. Macros, special forms (which are sort > of like system-internal macros and are used to build all the other > macros, and functions), Java constructors, Java methods, and functions > are callable (and maps and keywords -- also vectors -- act as > functions for this purpose). > > The only real overloading always involves macros: > > #() evaluates to a function and doesn't run its insides right away. > Then again so does (defn foo [x] (inc x)) -- the (inc x) is run when > foo is called, calling inc, but not when the (defn ...) is called. > Macros can delay evaluation of their contents, and #() is a reader > macro. > > '(x y z) is another reader macro and expands to (quote (x y z)). This was pretty much what I tried to explain as well, even including the comment that I almost never used '( ) in clojure because vectors worked as well. > > Mike also points out that things that aren't functions (not used in > > that context) can't be aliased with def or use. > > Really? > > user=> (def a 3) > #'user/a > user=> (def b a) > #'user/b > user=> b > 3 This one I flubbed, because my vocabulary failed me. There are three classes of values that can work when they show up in the first position in an executable expression: 1) Functions, which can also be passed to higher order functions. 2) Macros, which can't, but can be aliased by def or use. 3) Java interop things (#6 6 & 7 on his list), which can't be aliased by def or use. <mike -- Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html Independent Network/Unix/Perforce consultant, email for more information. O< ascii ribbon campaign - stop html mail - www.asciiribbon.org -- 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 Note that posts from new members are moderated - please be patient with your first post. 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
