extend srange, BEGINNING, END, FIRST, and LAST to strings

CHANGES.md

@@ -6,6 +6,7 @@
 * Added `traverse-all` which returns a transducer that traverses over all elements matching the given path.
 * `select-first` and `select-any` now avoid traversal beyond the first value matched by the path (like when using `ALL`), so they are faster now for those use cases.
 * Add `NAME` and `NAMESPACE` navigators
+* Extend `srange`, `BEGINNING`, `END`, `FIRST`, and `LAST` on strings to navigate to substrings
 * Improved `ALL` performance for PersistentHashSet
 * Dynamic navs automatically compile sequence returns if completely static
 * Eliminate reflection warnings for clj (thanks @mpenet)

src/clj/com/rpl/specter.cljc

@@ -706,10 +706,12 @@
   BEGINNING
   []
   (select* [this structure next-fn]
-    (next-fn []))
+    (next-fn (if (string? structure) "" [])))
   (transform* [this structure next-fn]
-    (let [to-prepend (next-fn [])]
-      (n/prepend-all structure to-prepend))))
+    (if (string? structure)
+      (str (next-fn "") structure)
+      (let [to-prepend (next-fn [])]
+        (n/prepend-all structure to-prepend)))))
 
 
 (defnav
@@ -717,11 +719,12 @@
   END
   []
   (select* [this structure next-fn]
-    (next-fn []))
+    (next-fn (if (string? structure) "" [])))
   (transform* [this structure next-fn]
-    (let [to-append (next-fn [])]
-      (n/append-all structure to-append))))
-
+    (if (string? structure)
+      (str structure (next-fn ""))
+      (let [to-append (next-fn [])]
+        (n/append-all structure to-append)))))
 
 (defnav
   ^{:doc "Navigates to the specified subset (by taking an intersection).

src/clj/com/rpl/specter/impl.cljc

@@ -521,14 +521,21 @@
 (mk-comp-navs)
 
 (defn srange-transform* [structure start end next-fn]
-  (let [structurev (vec structure)
-        newpart (next-fn (-> structurev (subvec start end)))
-        res (concat (subvec structurev 0 start)
-                    newpart
-                    (subvec structurev end (count structure)))]
-    (if (vector? structure)
-      (vec res)
-      res)))
+  (if (string? structure)
+    (let [newss (next-fn (subs structure start end))]
+      (str (subs structure 0 start)
+           newss
+           (subs structure end (count structure))
+           ))
+    (let [structurev (vec structure)
+          newpart (next-fn (-> structurev (subvec start end)))
+          res (concat (subvec structurev 0 start)
+                      newpart
+                      (subvec structurev end (count structure)))]
+      (if (vector? structure)
+        (vec res)
+        res
+        ))))
 
 (defn- matching-indices [aseq p]
   (keep-indexed (fn [i e] (if (p e) i)) aseq))

src/clj/com/rpl/specter/navs.cljc

@@ -298,7 +298,11 @@
 
 
 (defn srange-select [structure start end next-fn]
-  (next-fn (-> structure vec (subvec start end))))
+  (next-fn
+    (if (string? structure)
+      (subs structure start end)
+      (-> structure vec (subvec start end))
+      )))
 
 (def srange-transform i/srange-transform*)
 
@@ -430,6 +434,15 @@
         (let [i (dec c)]
           (assoc v i (afn (nth v i)))))))
 
+  #?(:clj String :cljs string)
+  (update-first [s afn]
+    (str (afn (nth s 0)) (subs s 1 (count s))))
+
+  (update-last [s afn]
+    (let [last-idx (-> s count dec)]
+      (str (subs s 0 last-idx) (afn (nth s last-idx)))
+      ))
+
   #?(:clj Object :cljs default)
   (update-first [l val]
     (update-first-list l val))
@@ -443,11 +456,19 @@
     (nth v 0))
   (get-last [v]
     (peek v))
+
   #?(:clj Object :cljs default)
   (get-first [s]
     (first s))
   (get-last [s]
-    (last s)))
+    (last s))
+
+  #?(:clj String :cljs string)
+  (get-first [s]
+    (nth s 0))
+  (get-last [s]
+    (nth s (-> s count dec))
+    ))
 
 
 

test/com/rpl/specter/core_test.cljc

@@ -1419,3 +1419,16 @@
   (= 'a/e (setval s/NAMESPACE "a" 'e))
   (= 'a/e (setval s/NAMESPACE "a" 'f/e))
   )
+
+(deftest string-navigation-test
+  (= "ad" (setval (s/srange 1 4) "" "abcd"))
+  (= "bc" (select-any (s/srange 1 4) "abcd"))
+  (= "ab" (setval s/END "b" "a"))
+  (= "ba" (setval s/BEGINNING "b" "a"))
+  (= "" (select-any s/BEGINNING "abc"))
+  (= "" (select-any s/END "abc"))
+  (= \a (select-any s/FIRST "abc"))
+  (= \c (select-any s/LAST "abc"))
+  (= "qbc" (setval s/FIRST \q "abc"))
+  (= "abq" (setval s/FIRST "q" "abc"))
+  )