add before-index and index-nav navigators

src/clj/com/rpl/specter.cljc

@@ -936,6 +936,60 @@
   nthpath
   (eachnav n/nthpath*))
 
+(defrichnav
+  ^{:doc "Navigates to the empty space between the index and the prior index. For select
+          navigates to NONE, and transforms to non-NONE insert at that position."}
+  before-index
+  [index]
+  (select* [this vals structure next-fn]
+    NONE)
+  (transform* [this vals structure next-fn]
+    (let [v (next-fn vals NONE)]
+      (if (identical? NONE v)
+        structure
+        ;; TODO: make a more efficient impl
+        (setval (srange index index) [v] structure)
+        ))))
+
+(defrichnav
+  ^{:doc "Navigates to the index of the sequence if within 0 and size. Transforms move element
+          at that index to the new index, shifting other elements in the sequence."}
+  index-nav
+  [i]
+  (select* [this vals structure next-fn]
+    (if (and (>= i 0) (< i (count structure)))
+      (next-fn vals i)
+      NONE
+      ))
+  (transform* [this vals structure next-fn]
+    (if (and (>= i 0) (< i (count structure)))
+      (let [newi (next-fn vals i)]
+        (if (= newi i)
+          structure
+          (let [v (select-any (nthpath i) structure)]
+            (if (vector? structure)
+              (let [shifted (if (< newi i)
+                              (loop [j (dec i)
+                                     s structure]
+                                (if (< j newi)
+                                  s
+                                  (recur (dec j) (assoc s (inc j) (nth s j)))
+                                  ))
+                              (loop [j (inc i)
+                                     s structure]
+                                (if (> j newi)
+                                  s
+                                  (recur (inc j) (assoc s (dec j) (nth s j)))
+                                  )))]
+                (assoc shifted newi v)
+                )
+                (->> structure
+                     (setval (nthpath i) NONE)
+                     (setval (before-index newi) v)
+                     )))))
+      structure
+      )))
+
 (defrichnav
   ^{:doc "Navigates to result of running `afn` on the currently navigated value."}
   view

test/com/rpl/specter/core_test.cljc

@@ -1587,6 +1587,36 @@
   (is (= 2 (binding [*dvar* :b] (dvar-tester))))
   )
 
+(deftest before-index-test
+  (let [data [1 2 3]
+        datal '(1 2 3)]
+    (is (predand= vector? [:a 1 2 3] (setval (s/before-index 0) :a data)))
+    (is (predand= vector? [1 2 3] (setval (s/before-index 1) s/NONE data)))
+    (is (predand= vector? [1 :a 2 3] (setval (s/before-index 1) :a data)))
+    (is (predand= vector? [1 2 3 :a] (setval (s/before-index 3) :a data)))
+    (is (predand= list? '(:a 1 2 3) (setval (s/before-index 0) :a datal)))
+    (is (predand= list? '(1 :a 2 3) (setval (s/before-index 1) :a datal)))
+    (is (predand= list? '(1 2 3 :a) (setval (s/before-index 3) :a datal)))
+    ))
+
+(deftest index-nav-test
+  (let [data [1 2 3 4 5 6]
+        datal '(1 2 3 4 5 6)]
+    (is (predand= vector? [3 1 2 4 5 6] (setval (s/index-nav 2) 0 data)))
+    (is (predand= vector? [1 3 2 4 5 6] (setval (s/index-nav 2) 1 data)))
+    (is (predand= vector? [1 2 3 4 5 6] (setval (s/index-nav 2) 2 data)))
+    (is (predand= vector? [1 2 4 5 3 6] (setval (s/index-nav 2) 4 data)))
+    (is (predand= vector? [1 2 4 5 6 3] (setval (s/index-nav 2) 5 data)))
+    (is (predand= vector? [6 1 2 3 4 5] (setval (s/index-nav 5) 0 data)))
+
+    (is (predand= list? '(3 1 2 4 5 6) (setval (s/index-nav 2) 0 datal)))
+    (is (predand= list? '(1 3 2 4 5 6) (setval (s/index-nav 2) 1 datal)))
+    (is (predand= list? '(1 2 3 4 5 6) (setval (s/index-nav 2) 2 datal)))
+    (is (predand= list? '(1 2 4 5 3 6) (setval (s/index-nav 2) 4 datal)))
+    (is (predand= list? '(1 2 4 5 6 3) (setval (s/index-nav 2) 5 datal)))
+    (is (predand= list? '(6 1 2 3 4 5) (setval (s/index-nav 5) 0 datal)))
+    ))
+
 #?(:clj
   (do
     (defprotocolpath FooPP)