Why (defn- ...) but (def ^:private? ...)

[Stig Brautaset]

Is it because the def form can also be ^:dynamic?

At any rate, I did an attempt at my first macro to create a (def- ...) form, but it doesn't seem to work. Can you not attach metadata in a macro?

(defmacro def-
  "Why (defn- private-fn ...) but (def ^:private var ...)?"
  [sym & body]
  `(def ^:private ~sym ~@body))

;; => #'user/def-
user> (macroexpand '(def- blah "foo bar quux"))
;; => (def blah "foo bar quux")

Stig

[Colin Yates]

Have you tried with-meta?

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[Herwig Hochleitner]

2015-05-07 16:12 GMT+02:00 Stig Brautaset <sbrau...@gmail.com>:

Is it because the def form can also be ^:dynamic?

Hm, cognitect turned it down, because basically "if you go down this road, why stop with def- ? and before you know, you've got a core namespace full of def*-" 

At any rate, I did an attempt at my first macro to create a (def- ...) form, but it doesn't seem to work. Can you not attach metadata in a macro?

You can, but it works differently than in normal source. Remember, that ^ attaches metadata the literal, that you annotate. so ^:private ~sym is the symbol ~sym with a private metadata key. The quasiquoting, however, rebuilds the form and inserts the sym parameter in place of the ~sym form. So to attach the metadata to actual def'ed symbol, you need to attach it to the output, the macro generates, like this: `(def ~(with-meta sym {:private true}) ...)

[adrian...@mail.yu.edu]

Reader macros are evaluated at read time, not macroexpansion time. Read time happens during reading - the process in which the characters in a file are read into the Lisp forms Clojure supports. Therefore ^:private is not syntax which can be manipulated in a macro, because by the point the macro is evaluated that form is no longer present. 

Check out the source for defn- (you can find it in a REPL by calling (clojure.repl/source defn-)

(defmacro defn-

  "same as defn, yielding non-public def"

  {:added "1.0"}

  [name & decls]

  (list* `defn (with-meta name (assoc (meta name) :private true)) decls))

(defmacro def-

  "same as def, yielding non-public def"

  ([name] `(def- ~name nil))

  ([name expr]

   (list `def (with-meta name (assoc (meta name) :private true)) expr)))

  

[Stig Brautaset]

Hi Herwig,

On Thursday, 7 May 2015 15:36:44 UTC+1, Herwig Hochleitner wrote:

2015-05-07 16:12 GMT+02:00 Stig Brautaset <sbrau...@gmail.com>:

Is it because the def form can also be ^:dynamic?

Hm, cognitect turned it down, because basically "if you go down this road, why stop with def- ? and before you know, you've got a core namespace full of def*-" 

And that is a fine justification :-) I was just curious.

 

Can you not attach metadata in a macro?

You can, but it works differently than in normal source. Remember, that ^ attaches metadata the literal, that you annotate. so ^:private ~sym is the symbol ~sym with a private metadata key. The quasiquoting, however, rebuilds the form and inserts the sym parameter in place of the ~sym form. So to attach the metadata to actual def'ed symbol, you need to attach it to the output, the macro generates, like this: `(def ~(with-meta sym {:private true}) ...)

Thank you for this explanation, it makes sense now!

Stig

[Leon Grapenthin]

Do you have a link to the discussion? Is this really the reasoning? 

I find it insufficient, because there aren't many defs supporting private :

def, defn, defmacro and definline if I am remembering correctly.

I am kind of tired of writing def ^:private. def- would really be nice to have. defmacro- as well. 

Is there a JIRA ticket about this?

[Andy Fingerhut]

I am not aware of any JIRA ticket for this, but there could be one lurking there somewhere.

Here is a link to a previous discussion about it on this group: https://groups.google.com/d/msg/clojure/r_ym-h53f1E/y1S31QXNhcAJ

Andy

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