Clojure

RFC: Anonymous functions interaction with -> and ->> threading macros

Details

  • Type: Enhancement Enhancement
  • Status: Closed Closed
  • Priority: Minor Minor
  • Resolution: Declined
  • Affects Version/s: Release 1.6
  • Fix Version/s: None
  • Component/s: None
  • Labels:
    None

Description

This is more of a starting point for discussion than a feature request. It'd be easy to write and submit the patch, but I want to ask if it's a good idea, since it would alter the semantics of two core macros, '> and '>>; and if it is a good idea, what considerations need to be balanced.

For threading macros, I'd like to special-case forms that begin with 'fn and 'fn*. It's often useful (but maybe a bad idea; that's why I'd like to start the discussion) to use the threading macros in conjunction with anonymous functions in addition to forms, like so (contrived example):

(defn sigmoid [x] (-> x 
                      - 
                      Math/exp 
                      (+ 1) 
                      #(/ 1 %)))

This won't compile; #(/ 1 %) expands to the form

(fn* [p1__1389#] (/ 1 p1__1389#))

modulo gensym, of course. The threading macro, not treating fn* and fn specially, alters that to:

(fn* (clojure.core/-> (clojure.core/-> (clojure.core/-> x -) Math/exp) (+ 1)) [p1__1417#] (/ 1 p1__1417#))

which is a fn* with a non-symbol (illegal label) before its binding vector, raising an error.

Is this worth "fixing", or are the benefits to small to justify the added complexity of a special case in the ->, ->> threading macros?

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  • Created:
    Updated:
    Resolved: