From c233fb7e9dd903a941249854abd348fc13ce7b7b Mon Sep 17 00:00:00 2001
From: nathanmarz <nathan@nathanmarz.com>
Date: Wed, 16 Aug 2017 07:28:05 -0400
Subject: [PATCH] add indexed-vals

---
 CHANGES.md                          |  1 +
 src/clj/com/rpl/specter.cljc        | 20 +++++++++++++-------
 test/com/rpl/specter/core_test.cljc |  2 ++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index fbf4f24..40895b5 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,6 @@
 ## 1.0.4-SNAPSHOT
 
+* Add `indexed-vals` navigator, a variant of `INDEXED-VALS` that allows for a customized start index.
 * Bug fix: Fix `INDEXED-VALS` invalidly overwriting elements in some transforms involving multiple index changes
 
 ## 1.0.3
diff --git a/src/clj/com/rpl/specter.cljc b/src/clj/com/rpl/specter.cljc
index c9f5feb..d7dc472 100644
--- a/src/clj/com/rpl/specter.cljc
+++ b/src/clj/com/rpl/specter.cljc
@@ -995,14 +995,14 @@
       )))
 
 (defnav
-  ^{:doc "Navigate to [index elem] pairs for each element in a sequence. Changing index in transform
-          has same effect as `index-nav`. Indices seen during transform take into account any shifting
-          from prior sequence elements changing indices."}
-  INDEXED-VALS
-  []
+  ^{:doc "Navigate to [index elem] pairs for each element in a sequence. The sequence will be indexed
+          starting from `start`. Changing index in transform has same effect as `index-nav`. Indices seen
+          during transform take into account any shifting from prior sequence elements changing indices."}
+  indexed-vals
+  [start]
   (select* [this structure next-fn]
     ;; could be more efficient with a primitive mutable field
-    (let [i (i/mutable-cell -1)]
+    (let [i (i/mutable-cell (dec start))]
       (doseqres NONE [e structure]
         (i/update-cell! i inc)
         (next-fn [(i/get-cell i) e])
@@ -1012,7 +1012,8 @@
       (reduce
        (fn [s e]
          (let [curri (first (i/get-cell indices))
-               [newi newe] (next-fn [curri e])]
+               [newi* newe] (next-fn [(+ start curri) e])
+               newi (- newi* start)]
            (i/update-cell!
              indices
              (fn [ii]
@@ -1029,6 +1030,11 @@
        structure
        ))))
 
+(def
+  ^{:doc "`indexed-vals` with a starting index of 0."}
+  INDEXED-VALS
+  (indexed-vals 0))
+
 (defrichnav
   ^{:doc "Navigates to result of running `afn` on the currently navigated value."}
   view
diff --git a/test/com/rpl/specter/core_test.cljc b/test/com/rpl/specter/core_test.cljc
index eab7f1a..58c015c 100644
--- a/test/com/rpl/specter/core_test.cljc
+++ b/test/com/rpl/specter/core_test.cljc
@@ -1626,6 +1626,8 @@
     (is (= [:a :b :c :d :e] (transform [s/INDEXED-VALS s/FIRST odd?] inc data)))
     (is (= [0 2 2 4] (transform [s/INDEXED-VALS s/LAST odd?] inc [0 1 2 3])))
     (is (= [0 1 2 3] (transform [s/INDEXED-VALS (s/collect-one s/LAST) s/FIRST] (fn [i _] i) [2 1 3 0])))
+    (is (= [-1 0 1 2 3] (transform [(s/indexed-vals -1) (s/collect-one s/LAST) s/FIRST] (fn [i _] i) [3 -1 0 2 1])))
+    (is (= [[1 :a] [2 :b] [3 :c]] (select (s/indexed-vals 1) [:a :b :c])))
     ))
 
 #?(:clj