Add Zipper.find_value/3 (#161)

lib/sourceror/zipper.ex

@@ -726,6 +726,24 @@ defmodule Sourceror.Zipper do
     end
   end
 
+  @spec find_value(t, (tree -> any)) :: any | nil
+  def find_value(%Z{} = zipper, direction \\ :next, fun)
+      when direction in [:next, :prev] and is_function(fun, 1) do
+    do_find_value(zipper, move(direction), fun)
+  end
+
+  defp do_find_value(nil, _move, _fun), do: nil
+
+  defp do_find_value(%Z{node: tree} = zipper, move, fun) do
+    result = fun.(tree)
+
+    if result do
+      result
+    else
+      zipper |> move.() |> do_find_value(move, fun)
+    end
+  end
+
   defp move(:next), do: &next/1
   defp move(:prev), do: &prev/1
 

test/zipper_test.exs

@@ -571,6 +571,66 @@ defmodule SourcerorTest.ZipperTest do
     end
   end
 
+  describe "find_value/3" do
+    test "finds a zipper and returns the value" do
+      zipper = Z.zip([1, [2, [3, 4], 5]])
+
+      assert Z.find_value(zipper, fn
+               4 -> 4
+               _ -> false
+             end) == 4
+
+      assert Z.find_value(zipper, :next, fn
+               4 -> 4
+               _ -> false
+             end) == 4
+    end
+
+    test "returns nil if nothing was found" do
+      zipper = Z.zip([1, [2, [3, 4], 5]])
+
+      assert Z.find_value(zipper, fn
+               9 -> 9
+               _ -> false
+             end) == nil
+
+      assert Z.find_value(zipper, :prev, fn
+               9 -> 9
+               _ -> false
+             end) == nil
+    end
+
+    test "finds a zipper with a predicate in direction :prev" do
+      zipper =
+        [1, [2, [3, 4], 5]]
+        |> Z.zip()
+        |> Z.next()
+        |> Z.next()
+        |> Z.next()
+        |> Z.next()
+
+      assert Z.find_value(zipper, :prev, fn
+               2 -> 2
+               _ -> false
+             end) == 2
+    end
+
+    test "retruns nil if nothing was found in direction :prev" do
+      zipper =
+        [1, [2, [3, 4], 5]]
+        |> Z.zip()
+        |> Z.next()
+        |> Z.next()
+        |> Z.next()
+        |> Z.next()
+
+      assert Z.find_value(zipper, :prev, fn
+               9 -> 9
+               _ -> false
+             end) == nil
+    end
+  end
+
   describe "subtree/1" do
     test "returns a new zipper isolated on the focused of the parent zipper" do
       zipper =