feat: add x-group

lens.lisp

@@ -423,6 +423,11 @@
                       (reverse (cdr it))))
               (alexandria:hash-table-alist groups)))))
 
+(defun x-group (fn)
+  (lambda (groups)
+    (loop for (key . group) in groups
+          collect (funcall fn key group))))
+
 (defun hash-join (probe join-fn &key (test 'eql) (key 'car))
   (let* ((lookup (make-hash-table :test test :size (length probe)))
          (lookup-fn (functionalize lookup)))

package.lisp

@@ -21,9 +21,7 @@
            #:transform-elt #:denest #:op #:defalias #:<> #:<>1 #:== #:•
            #:∘ #:suffixp #:functionalize #:inc #:group-by #:keys
            #:conj #:disj #:delay #:of-type #:transform #:calling*
-           #:calling
-           #:hash-join
-           #:tap))
+           #:calling #:hash-join #:tap #:x-group))
 
 (defpackage :data-lens.transducers.internals
   (:use :cl)