implement reduce builtin

src/ruby/ycp/builtins.rb

@@ -320,14 +320,16 @@ def self.flatten value
 
     module List
       # Reduces a list to a single value.
-      def self.reduce
-        raise "Builtin list::reduce() is not implemented yet"
+      def self.reduce *params, &block
+        return nil if params.first.nil?
+        list = params.first
+        if params.size == 2
+          return nil if params[1].nil?
+          list = [list] + params[1]
+        end
+        return list.reduce &block
       end
 
-      # Reduces a list to a single value.
-      def self.reduce
-        raise "Builtin list::reduce() is not implemented yet"
-      end
 
       # Creates new list with swaped elemetns at offset i1 and i2.
       def self.swap

tests/ruby/builtins_test.rb

@@ -515,4 +515,39 @@ def test_flatten
       assert_equal result, YCP::Builtins.flatten(value)
     end
   end
+
+  def test_list_reduce_1param
+    list = [0,1,2,3,2,1,-5]
+    res = YCP::Builtins::List.reduce(list) do |x,y|
+      next x>y ? x : y
+    end
+
+    assert_equal 3, res
+
+    res = YCP::Builtins::List.reduce(list) do |x,y|
+      next x + y
+    end
+    assert_equal 4, res
+
+    assert_equal nil, YCP::Builtins::List.reduce([]) { |x,y| next x }
+    assert_equal nil, YCP::Builtins::List.reduce(nil) { |x,y| next x }
+  end
+
+  def test_list_reduce_2params
+    list = [0,1,2,3,2,1,-5]
+    res = YCP::Builtins::List.reduce(15,list) do |x,y|
+      next x>y ? x : y
+    end
+
+    assert_equal 15, res
+
+    res = YCP::Builtins::List.reduce(15,list) do |x,y|
+      next x + y
+    end
+
+    assert_equal 19, res
+
+    assert_equal 5, YCP::Builtins::List.reduce(5,[]) { |x,y| next x }
+    assert_equal nil, YCP::Builtins::List.reduce(nil,nil) { |x,y| next x }
+  end
 end