fix zipper navigation to stop navigating when right/left/up/down/next navigate nowhere

DEVELOPER.md

@@ -8,6 +8,7 @@ lein cleantest
 
 ```
 rm -rf out/
+lein cljx
 rlwrap java -cp `lein classpath` clojure.main repl.clj
 (require 'com.rpl.specter.cljs-test-runner)
 ```

src/clj/com/rpl/specter/zipper.cljx

@@ -1,10 +1,10 @@
 (ns com.rpl.specter.zipper
   #+cljs (:require-macros
             [com.rpl.specter.macros
-              :refer [defpath]])
+              :refer [defpath path]])
   #+clj
   (:use
-    [com.rpl.specter.macros :only [defpath]])
+    [com.rpl.specter.macros :only [defpath path]])
   (:require [com.rpl.specter :as s]
             [clojure.zip :as zip]))
 
@@ -19,13 +19,37 @@
 (def SEQ-ZIP (zipper zip/seq-zip))
 (def XML-ZIP (zipper zip/xml-zip))
 
-(def NEXT (s/view zip/next))
-(def RIGHT (s/view zip/right))
+
+(def NEXT
+  (s/comp-paths
+    (s/view zip/next)
+    (s/if-path zip/end?
+      s/STOP
+      s/STAY)))
+
+(defn- mk-zip-nav [nav]
+  (path []
+    (select* [this structure next-fn]
+      (let [ret (nav structure)]
+        (if ret (next-fn ret))
+        ))
+    (transform* [this structure next-fn]
+      (let [ret (nav structure)]
+        (if ret (next-fn ret) structure)
+        ))))
+
+;; (multi-path RIGHT LEFT) will not navigate to the right and left
+;; of the currently navigated element because locations aren't stable
+;; like they are for maps/graphs. The path following RIGHT could 
+;; insert lots of elements all over the sequence, and there's no
+;; way to determine how to get "back". 
+(def RIGHT (mk-zip-nav zip/right))
+(def LEFT (mk-zip-nav zip/left))
+(def DOWN (mk-zip-nav zip/down))
+(def UP (mk-zip-nav zip/up))
+
 (def RIGHTMOST (s/view zip/rightmost))
-(def LEFT (s/view zip/left))
-(def DOWN (s/view zip/down))
 (def LEFTMOST (s/view zip/leftmost))
-(def UP (s/view zip/up))
 
 (defn- inner-insert [structure next-fn inserter mover backer]
   (let [to-insert (next-fn [])

test/com/rpl/specter/zipper_test.cljx

@@ -3,11 +3,15 @@
            [cljs.test :refer [is deftest]]
            [cljs.test.check.cljs-test :refer [defspec]]
            [com.rpl.specter.cljs-test-helpers :refer [for-all+]]
+           [com.rpl.specter.macros
+             :refer [declarepath providepath]]
            )
   (:use
     #+clj [clojure.test :only [deftest is]]
     #+clj [clojure.test.check.clojure-test :only [defspec]]
     #+clj [com.rpl.specter.test-helpers :only [for-all+]]
+    #+clj [com.rpl.specter.macros
+           :only [declarepath providepath]]
     )
   (:require #+clj [clojure.test.check.generators :as gen]
             #+clj [clojure.test.check.properties :as prop]
@@ -64,3 +68,31 @@
            [1 [2 3 4] 5]
            )))
   )
+
+(declarepath NEXT-WALKER)
+
+(providepath NEXT-WALKER
+  (s/stay-then-continue
+    z/NEXT
+    NEXT-WALKER
+    ))
+
+
+(deftest next-terminate-test
+  (is (= [2 [3 4 [5]] 6]
+         (s/transform [z/VECTOR-ZIP NEXT-WALKER z/NODE number?]
+           inc
+           [1 [2 3 [4]] 5])))
+  )
+
+(deftest zipper-nav-stop-test
+  (is (= [1]
+         (s/transform [z/VECTOR-ZIP z/UP z/NODE] inc [1])))
+  (is (= [1]
+         (s/transform [z/VECTOR-ZIP z/DOWN z/LEFT z/NODE] inc [1])))
+  (is (= [1]
+         (s/transform [z/VECTOR-ZIP z/DOWN z/RIGHT z/NODE] inc [1])))
+  (is (= []
+         (s/transform [z/VECTOR-ZIP z/DOWN z/NODE] inc [])))
+  )
+