Implement Named over Vars

Question

Vars, while a general reference structure, are used to implement bindings and have special reader and printer notation reflecting this reality. Unlike Keywords and Symbols which share the "namespace/name" notation of Vars, Vars do not implement the clojure.lang.Named interface while they print as if they were Named.

The attached patch implements Named over Vars.

Example:

`
user=> (name :clojure.core/conj)
"conj"
user=> (namespace :clojure.core/conj)
"clojure.core"
user=> (name 'clojure.core/conj)
"conj"
user=> (namespace 'clojure.core/conj)
"clojure.core"
user=> (name #'clojure.core/conj)
"conj"
user=> (namespace #'clojure.core/conj)
"clojure.core"
user=> (with-local-vars [x 1] (name x))
"--unnamed--"
user=> (with-local-vars [x 1] (namespace x))
nil
user=> (with-local-vars [x 1] (println x))

<Var: --unnamed-->

`

This is useful for applications such as the CinC project where Vars are often taken directly as values in which context they would ideally be interchangeable with the Symbols the bound values of which they represent.

Answer 1

Comment made by: bronsa

With this patch calling name on a unnamed Var will cause a NPE, I don't think this is desiderable.

Answer 2

Comment made by: arrdem

I agree, however this behavior seems to be standard in Core.

Clojure 1.6.0
user=> (name nil)
NullPointerException clojure.core/name (core.clj:1518)
user=> (namespace nil)
NullPointerException clojure.core/namespace (core.clj:1526)

I'm also not convinced that the "name" or "namespace" of an unbound var is meaningful, in which case a NPE is probably acceptable.

Answer 3

Comment made by: bronsa

I was not talking about unbound Vars, but about anonymous Vars, I'm assuming you miswrote.

I'd agree with you that throwing an exception could be a reasonable behaviour, except I can test for nil before calling name on it while there's no way to test whether a var is named or not, except trying to access directly the .name field which is excatly what this ticket is for.

Answer 4

Comment made by: bronsa

Me and Reid have been talking about this issue over IRC, here's what's come up:
Vars can be either unnamed (as are Vars returned by with-local-vars) or contain both a namespace and a name part( that's the case for interned Vars)
there's currently no way to test for the "internedness" of a Var, so accessing either the .name or the .namespace field of the Var testing for nil is the only way to do it currently

given the above, the current patch seems unsatisfactory, here some proposed solutions:
make Var Named, make namespace return nil for an unnamed Var and name return "--unnamed--"
keep Var not implementing Named, add a "var-symbol" function returning either a namespaced symbol matching the ns+name of the Var or nil for an unnamed Var

Personally, I'd rather have the second solution implemented as I don't feel Var should be Named given that they can be unnamed and that strikes me as a contradicion

Answer 5

Comment made by: arrdem

Added patches explicitly handling the unnamed var cases.

Answer 6

Comment made by: arrdem

Squashed all patches into a single diff and updated attachments.

Answer 7

Reference: https://clojure.atlassian.net/browse/CLJ-1488 (reported by arrdem)