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