Thanks -- interesting, especially the bit about the design notes on a compiler rewrite.
On Thu, Apr 21, 2011 at 22:23, Kevin Downey <redc...@gmail.com> wrote: > the current compiler doesn't namespace qualify special forms (forms > which are built into the compiler) but somethings that the > documentation lists as "special forms" are infact macros defined in > clojure.core based on the real special forms provided by the compiler. > macros are namespace qualified so unless you use the fully qualified > name(clojure.core/let) or :use/use them then they aren't available. > this difference is kind of unfortunate, and the design notes on a > compiler rewrite mention changing things so the forms directly > supported by the compiler are also namespace qualified and live in > clojure.core > > On Thu, Apr 21, 2011 at 12:24 PM, Simon Katz <nomisk...@gmail.com> wrote: > > Hi. > > > > (In case it makes a difference, I'm using Clojure 1.2.) > > > > If one creates a new namespace using in-ns, the new namespace > > does not refer to clojure.core, as explained at > > http://clojure.org/namespaces. > > > > I noticed one can use certain special forms in a namespace > > created using in-ns, but not others: > > _________________________________________ > > | > > | user> (in-ns 'my-new-ns) > > | #<Namespace my-new-ns> > > | > > | my-new-ns> (quote a) > > | a > > | > > | my-new-ns> (def x 42) > > | #'my-new-ns/x > > | > > | my-new-ns> (let [a 42] a) > > | ;; Evaluation aborted. Unable to resolve symbol: let in this context > > | > > | my-new-ns> (fn [] 42) > > | ;; Evaluation aborted. Unable to resolve symbol: fn in this context > > |_________________________________________ > > > > That puzzled me. > > > > In the process of trying to understand, I came across a mention > > of clojure.lang.Compiler/specials (a map with symbols as its keys) > > at > http://stackoverflow.com/questions/3159836/is-there-a-way-to-get-a-collection-of-clojure-special-forms-programatically > > _________________________________________ > > | > > | user> (keys clojure.lang.Compiler/specials) > > | ;; => (deftype* new quote & var set! monitor-enter recur . > > | case* clojure.core/import* reify* do fn* throw > > | monitor-exit letfn* finally let* loop* try catch if > > | def) > > |_________________________________________ > > > > So it seems that there are two kinds of special symbol. I'll > > refer to them as implementation specials and documented specials: > > - implementation specials > > those that are keys in the clojure.lang.Compiler/specials > > map > > - documented specials > > those that are documented as being special at > > http://clojure.org/special_forms. > > (Note that some symbols are of both kinds.) > > > > I assume that documented specials that are not implementation > > specials are implemented as macros. (And the post I mentioned > > above at stackoverflow.com says so.) > > > > Here's some investigation of these two kinds of special symbol: > > _________________________________________ > > | > > | user> (def implementation-specials > > | (keys clojure.lang.Compiler/specials)) > > | #'user/implementation-specials > > | > > | user> (def documented-specials > > | '(def if do let quote var fn loop recur throw try > > | monitor-enter monitor-exit . new set!)) > > | #'user/documented-specials > > | > > | user> (defn symbol-info [symbol] > > | [(special-symbol? symbol) > > | (= (resolve symbol) nil) > > | symbol]) > > | #'user/symbol-info > > | > > | user> (pprint (map symbol-info implementation-specials)) > > | ([true true deftype*] > > | [true true new] > > | [true true quote] > > | [true true &] > > | [true true var] > > | [true true set!] > > | [true true monitor-enter] > > | [true true recur] > > | [true true .] > > | [true true case*] > > | [true true clojure.core/import*] > > | [true true reify*] > > | [true true do] > > | [true true fn*] > > | [true true throw] > > | [true true monitor-exit] > > | [true true letfn*] > > | [true true finally] > > | [true true let*] > > | [true true loop*] > > | [true true try] > > | [true true catch] > > | [true true if] > > | [true true def]) > > | nil > > | > > | user> (pprint (map symbol-info documented-specials)) > > | ([true true def] > > | [true true if] > > | [true true do] > > | [false false let] > > | [true true quote] > > | [true true var] > > | [false false fn] > > | [false false loop] > > | [true true recur] > > | [true true throw] > > | [true true try] > > | [true true monitor-enter] > > | [true true monitor-exit] > > | [true true .] > > | [true true new] > > | [true true set!]) > > | nil > > |_________________________________________ > > > > There are a few interesting things here: > > > > - special-symbol? returns true for implementation specials > > (actually not surprising when you look at the implementation > > of special-symbol?, but perhaps surprising if you have only > > read http://clojure.org/namespaces and the documentation of > > special-symbol? which says "Returns true if [the argument] > > names a special form"). > > > > - Calling resolve on an implementation special gives nil. > > > > - In a namespace created using in-ns (such as my-new-ns above) > > one is able to make use of implementation specials. > > Implementation specials seem to bypass the normal > > resolution process: > > - defn is not an implementation special: > > user> (resolve 'defn) > > #'clojure.core/defn > > - def is an implementation special: > > user> (resolve 'def) > > nil > > > > Well, that's probably enough wittering. > > > > Any comments? > > > > And my main question... > > Is any of this stuff documented? (Perhaps there's other related > > stuff that it would be good to know.) > > > > Simon > > > > -- > > 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 > > > > -- > And what is good, Phaedrus, > And what is not good— > Need we ask anyone to tell us these things? > > -- > 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. 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