Hello Konrad, many thanks, that clarifies it! So, in "A special form is always built in, and cannot be implemented in the language itself." the first part is true, the second is not. Like most lisps have a bilt in list-reverse for speed reasons. In that case, this build in thing is a special form that can also be implemented in the language (only slow). Right?
"A special form is named by a symbol whose interpretation cannot be overridden in any way." This explains the problem from another thread (that made me ask this question in the first place): user=> (def do println) #'user/do ; this uses the special form user=> (do "huhu" "plop") "plop" ; while this uses println user=> ((var do) "huhu" "hello") huhu hello nil Thank you, alux On 31 Mai, 10:38, Konrad Hinsen <konrad.hin...@fastmail.net> wrote: > On 31 May 2010, at 09:35, alux wrote: > > > I got a very basic question about the concept of "special form". What > > is correct, multiple selections allowed: > > > [ ] A special form is what can be implemented by a macro. > > Wrong. You cannot implement a Lisp-like language with just macros and > functions. At some point the operations defined by macros and > functions must be reduced to fundamental operations that are handled > directly by the compiler. > > Example: if and cond. You can implement either one in terms of the > other one as a macro, but you cannot implement *both* as macros. > > > [ ] Every macro gives a special form. > > Wrong. A macro rewrites a form to another form. A special form is > interpreted directly by the compiler. > > There is also a technical difference: a macro is the value of a name, > which is looked up in the context of the macro call. Constructs like > macrolet (clojure.contrib.macro-utils) permit local macro definitions, > for example. A special form is named by a symbol whose interpretation > cannot be overridden in any way. > > > [ ] Only a macro that doesn't evaluate some of its arguments gives a > > special form. > > Wrong as well. The distinction between macros and special forms is a > matter of implementation, not of evaluating arguments. > > > [ ] A special form is always built in, and cannot be implemented in > > the language itself. > > True for a minimalist language implementation. An implementation may > choose to use more special forms than strictly necessary for > performance reasons. > > > [ ] The concept of special form doesnt have anything to do with > > eagerness or lazyness. > > True. > > Konrad. -- 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
