On Mon, Mar 14, 2011 at 6:32 PM, Dominikus <dominikus.herzb...@gmail.com> wrote: > I did some investigations on the code in Compiler.java. There is an > IPersistentMap called 'specials' (line 95, Clojure 1.2) that maps > symbols like 'if' to parsers like IfExpr.Parser(); obviously, these > are the parsers recognizing special forms. > > Method analyzeSeq (line 5347) tries macro expansion first and gets the > operator of a sequence form next. There is some special behavior if > the operator is FN (namely 'fn*' for which no parser is associated in > 'specials'; I don't know why 'fn*' gets special treatment here), then > special parsers are activated if the operator is a special symbol, > otherwise InvokeExpr.parse() is run.
That doesn't quite seem right: user=> (defmacro if [x y] `(println ~x ~y)) #'user/if user=> (if (even? 42) "boo!") "boo!" user=> (user/if (even? 42) "boo!") true boo! nil user=> Clearly, the if special symbol, when in operator position, shadows even macros, forcing the use of a fully-qualified name to employ a macro named "if". Perhaps you meant it does macroexpansion of the subforms first, but not (yet) of the whole form? Then it checks for the whole form to be a special form; then for the whole form to be a macro in need of expansion; and then treats it as a function call. If so, it's only the subforms not in operator position that get macroexpanded first. Otherwise user=> (defmacro qqq [] 'if) #'user/qqq user=> ((qqq) (even? 42) "boo!") #<CompilerException java.lang.Exception: Unable to resolve symbol: if in this context (NO_SOURCE_FILE:607)> would instead produce "boo!", as (qqq) would be expanded to if and then (if (even? 42) "boo!") would be parsed and discovered to be an if special form. On the other hand, user=> (quote (qqq)) (qqq) seems to indicate that nothing is macroexpanded before special form parsing occurs, or it would have output if instead of (qqq), unless quote it another special case. -- 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
