Support arbitrary functional destructuring via -> and ->>

Question

Support arbitrary functional destructuring, that is the use of
any function in any destructuring form to help unpack data in
arbitrary ways.

The discussion began here:
http://clojure-log.n01se.net/date/2009-11-17.html#09:31c

The attached patch implements the spec described here:
http://clojure-log.n01se.net/date/2009-11-17.html#10:50a

That is, the following examples would now work:

user=> (let (link: (-> str a) 1) a)
"1"

user=> (let (link: [a (-> str b) c) (link: 1 2)] (list a b c))
(1 "2" nil)

user=> (let (link: (->> (map int) [a b)) "ab"] (list a b))
(97 98)

Answer 1

Comment made by: importer

cgrand said: I think the current patch suffers from the problem described here http://groups.google.com/group/clojure-dev/msg/80ba7fad2ff04708 too.

Answer 2

_Comment made by: importer_

cgrand said: Only -> and ->> are legal here but what if they are aliased or shadowed? Instead of testing the symboil per se I would check, if:
* the symbol is not in &env
* the symbol resolve to #'clojure.core/-> or  #'clojure.core/->>


(when-not (&env (first b)) (#{#'clojure.core/-> #'clojure.core/->>} (resolve (first b))))


but it requires to change destructure's sig to pass the env around

Answer 3

_Comment made by: importer_

[email protected] said: Only -> and ->> are actually legal here anyway -- if you've locally bound foo to -> there's not really any good reason to think (fn [(foo inc a)] a) should work.  And if you've redefined -> or ->> to mean something else in your ns, do we need to catch that at compile time, or is it okay to emit the rearranged code and see what happens?

In short, would '#{-> ->> clojure.core/-> clojure.core/->>} be sufficient?

Answer 4

Comment made by: importer

Converted from http://www.assembla.com/spaces/clojure/tickets/211
Attachments:
destructuring-fns.diff - https://www.assembla.com/spaces/clojure/documents/aHWQ_W06Kr3O89eJe5afGb/download/aHWQ_W06Kr3O89eJe5afGb

Answer 5

Comment made by: importer

[email protected] said: (link: [file:aHWQ_W06Kr3O89eJe5afGb)]: (link: PATCH) Support -> and ->> in destructuring forms.

Answer 6

Comment made by: importer

richhickey said: so, don't use syntax-quote, just use clojure.core/->

Answer 7

Comment made by: stu

Rich: Are you assigned to this by accident? If so, please deassign yourself.

Answer 8

Reference: https://clojure.atlassian.net/browse/CLJ-211 (reported by alex+import)