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[CLJ-1110] let-> needs improvement Created: 20/Nov/12  Updated: 11/Dec/12  Resolved: 29/Nov/12

Status: Closed
Project: Clojure
Component/s: None
Affects Version/s: Release 1.5
Fix Version/s: None

Type: Enhancement Priority: Major
Reporter: Alex Nixon Assignee: Unassigned
Resolution: Completed Votes: 0
Labels: None


The function clojure.core/let-> is suboptimal in a few regards:
1. It's name lends you to believe it is "let-like", but it is not - it does not take a binding form, and its arguments are 'backwards'
2. It's docstring doesn't make clear that it is intended for use solely in a threading-macro expression
3. It arbitrarily does not support destructuring, where it easily could.

Possible solutions:

  • rename it (e.g. to "bind->") to make clear it is not let-like
  • allow destructuring of the 'name' parameter

Google groups discussion: https://groups.google.com/d/topic/clojure/67JQ7xSUOM4/discussion

Comment by Yongqian Li [ 11/Dec/12 12:22 AM ]

Has it been decided whether as-> supports de-structuring or not? Right now it is inconsistent.

(as-> [0 1]
      [a b]
  [(inc a) (inc b)])

 => [1 2]

(as-> {:a 0 :b 1}
      {:keys [a b]}
  {:a (inc a) :b (inc b)})

 => {:keys [1 2]}
Comment by Yongqian Li [ 11/Dec/12 12:50 AM ]

Also, what about changing the name to >as? ->as reads like "pipeline as name", whereas as> implies that you are starting a new pipeline.

(-> 0
  (->as name 

Makes it clearer that you are consuming a pipeline and the expressions within ->as are no longer being influenced by ->.

Comment by Yongqian Li [ 11/Dec/12 1:03 AM ]

Has the addition of ->>as been considered? That way you can use it inside a ->> like this:

(->> a 
  (->>as name

(-> a 
  (->as name

The signature would be [name forms init-expr].

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