CL-Arrows

Implements the -> and ->> threading macros in Clojure, as well as -<> and -<>> from the swiss-arrows library.

This is an ASDF system providing the package cl-arrows.

Documentation

[macro]
-> initial-form &rest forms => results

Inserts INITIAL-FORM as first argument into the first of FORMS, the result into the next, etc., before evaluation. FORMS are treated as list designators.

[macro]
->> initial-form &rest forms => results

Like ->, but the forms are inserted as last argument instead of first.

[macro]
-<> initial-form &rest forms => results

Like ->, but if a form in FORMS has one or more symbols named <> as top-level element, each such symbol is substituted by the primary result of the form accumulated so far, instead of it being inserted as first argument. Also known as diamond wand.

[macro]
-<>> initial-form &rest forms => results

Like -<>, but if a form in FORMS has no symbols named <> as top-level element, insertion is done like in ->>. Also known as diamond spear.

Examples

(-> 3
    /)  ; insert into designated list (/)
=> 1/3

(-> 3
    (expt 2))  ; insert as first argument
=> 9

(->> 3
     (expt 2))  ; insert as last argument
=> 8

(-<>> (list 1 2 3)
      (remove-if #'oddp <> :count 1 :from-end t) ; substitute <>
      (reduce #'+)                               ; insert last
      /)                                         ; list designator
=> 1/3

(let ((x 3))
  (-<> (incf x)     ; (let ((r (incf x)))
       (+ <> <>)))  ;   (+ r r))
=> 8

Todo

Future versions might include further ideas from rplevy's swiss-arrows.