Improved variable definitions

src/build/expression/Expression.go

@@ -54,6 +54,23 @@ func (expr *Expression) Close() {
 	pool.Put(expr)
 }
 
+// EachLeaf iterates through all leaves in the tree.
+func (expr *Expression) EachLeaf(callBack func(*Expression) error) error {
+	if expr.IsLeaf() {
+		return callBack(expr)
+	}
+
+	for _, child := range expr.Children {
+		err := child.EachLeaf(callBack)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // RemoveChild removes a child from the expression.
 func (expr *Expression) RemoveChild(child *Expression) {
 	for i, c := range expr.Children {