"alux" <alu...@googlemail.com> said: > 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. Macros cannot remove the need for special-forms, at least not in a real interpreter. In a metacircular implementation, you can replace special-forms with calls to the base-level implementation. For instance, if you evaluate 'if' at base-level, then you can use it to define 'cond' at base-level. > [ ] Every macro gives a special form. They can all be reduced to a number of expressions that cannot be implemented by neither macros nor functions. These expressions can be evaluated using normal functions if you have lazy evaluation of arguments. So, if you have lazy-eval, there's no need for special-forms. > [ ] Only a macro that doesn't evaluate some of its arguments gives a > special form. You could say that. > [ ] A special form is always built in, and cannot be implemented in > the language itself. Unless you have lazy-eval. > [ ] Special forms are exactly the things that can be called, but dont > evaluate all of their arguments. (Macros and build-ins, at least for > eager languages.) > > [ ] The concept of special form doesnt have anything to do with > eagerness or lazyness. Wrong. It has everything to do with laziness. If you have one, you don't need the other. Please note that, the concept of special-forms is a compromise and I don't think anyone would want to have them. A language designer has to make a choice as to whether to have special forms or not. If they don't want special-forms, then they should provide lazy evaluation of arguments. Some introduce functional parameters in order to provide lazy evaluation of arguments but that choice has its own trade-offs since it introduces a kind of dynamic scoping. Kind regards, SinDoc -- 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
