Simple and efficient implementation of walk/1 (#2795)

src/builtin.jq

@@ -246,13 +246,14 @@ def bsearch($target):
 
 # Apply f to composite entities recursively, and to atoms
 def walk(f):
-  . as $in
-  | if type == "object" then
-      reduce keys_unsorted[] as $key
-        ( {}; . + { ($key):  ($in[$key] | walk(f)) } ) | f
-  elif type == "array" then map( walk(f) ) | f
-  else f
-  end;
+  def w:
+    if type == "object"
+    then map_values(w)
+    elif type == "array" then map(w)
+    else .
+    end
+    | f;
+  w;
 
 # pathexps could be a stream of dot-paths
 def pick(pathexps):