Shouldn't the "macro?" case have an (eval ...) wrapped around the (apply ...)?
On Sat, Jul 20, 2013 at 4:19 PM, Gary Verhaegen <gary.verhae...@gmail.com>wrote: > fn and let are macros in the clojure.core namespace; & is technically not > a valid character in a symbol, but the Clojure reader is quite lenient on > that front. As far as I know, it is not treated as anything special at the > level of the language, it is just interpreted by the destructuring macros. > > On the other hand, real "special forms" in the Lispy sense are not macros > - they are "hard coded". > > Think of the interpreter as doing something akin to: > > (defn eval [form) > (if (list? form) > (cond > (= 'let* (first form)) (...)) > (= 'fn* (first form)) (...)) > ;; same for all special forms > (fn? (get-in-env (first form))) (apply (first form) (map eval (rest > form))) > (macro? (get-in-env (first form))) (apply (first form) (rest > form)))))) > > This is of course highly sketchy, but you get the idea: functions and > macros are looked-up in the environment and executed from their definition, > so you can rebind them in the local environment, but special forms are just > executed directly. > > (At least, this is how it works in toy implementations à la SICP & little > schemer - I'm not at all familiar with the Clojure source code, but this is > a working mental model for explaining the observed behavior.) > > > On 24 June 2013 00:43, Ben Wolfson <wolf...@gmail.com> wrote: > >> Well, when used as the first element of a list. (And I certainly wouldn't >> use them as local names, since that would be extremely confusing; I was >> trying to verify the correctness of some code I'm working on.) >> >> But I called these "extra-special" because, in my understanding of the >> term, "special form" generically just refers to something with non-normal >> evaluation order (or special evaluation semantics generally). "when", in >> this definition, is a special form, as are "fn" and "let" (both of which >> are listed as special forms on http://clojure.org/special_forms). But >> neither "fn" nor "let" is special the way "let*", "fn*", "do", or the other >> *extra*-special forms are: >> >> user> (let [fn (fn [x] x)] (fn 4)) >> 4 >> user> (let [let (fn [x] x)] (let 4)) >> 4 >> >> Thinking about it more, I suppose you're thinking of what's returned by >> clojure.lang.Compiler/specials, except several of them can be used just >> fine in this pattern: >> >> user> (let [& (fn [x] x)] (& 1)) >> 1 >> >> The above also works for finally and catch. >> >> Anyway, I'm surprised one can establish local bindings for these guys at >> all. >> >> On Sun, Jun 23, 2013 at 2:46 PM, Ambrose Bonnaire-Sergeant < >> abonnaireserge...@gmail.com> wrote: >> >>> Special forms are special when used in a list. IMO it's a bad idea to >>> use special forms >>> as local names, a caveat which is surprisingly under-documented. >>> >>> Thanks, >>> Ambrose >>> >>> >>> On Mon, Jun 24, 2013 at 5:38 AM, Ben Wolfson <wolf...@gmail.com> wrote: >>> >>>> This strikes me as pretty odd: >>>> >>>> user> (let [z 1 >>>> try 2 >>>> fn* 3] >>>> (try (let [x (fn* ([a b c] [a b c]))] >>>> (x z try fn*)) >>>> (catch Exception e e))) >>>> [1 2 3] >>>> >>>> >>>> -- >>>> Ben Wolfson >>>> "Human kind has used its intelligence to vary the flavour of drinks, >>>> which may be sweet, aromatic, fermented or spirit-based. ... Family and >>>> social life also offer numerous other occasions to consume drinks for >>>> pleasure." [Larousse, "Drink" entry] >>>> >>>> -- >>>> -- >>>> 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 >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "Clojure" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to clojure+unsubscr...@googlegroups.com. >>>> For more options, visit https://groups.google.com/groups/opt_out. >>>> >>>> >>>> >>> >>> -- >>> -- >>> 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 >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to clojure+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >>> >>> >> >> >> >> -- >> Ben Wolfson >> "Human kind has used its intelligence to vary the flavour of drinks, >> which may be sweet, aromatic, fermented or spirit-based. ... Family and >> social life also offer numerous other occasions to consume drinks for >> pleasure." [Larousse, "Drink" entry] >> >> -- >> -- >> 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 >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> > > -- > -- > 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 > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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