diff --git a/examples/collatz/collatz.q b/examples/collatz/collatz.q
new file mode 100644
index 0000000..3093312
--- /dev/null
+++ b/examples/collatz/collatz.q
@@ -0,0 +1,22 @@
+import log
+import sys
+
+main() {
+	x := 12
+
+	loop {
+		if x & 1 == 0 {
+			x /= 2
+		} else {
+			x = 3 * x + 1
+		}
+
+		log.number(x)
+
+		if x == 1 {
+			return
+		}
+
+		sys.write(1, " ", 1)
+	}
+}
\ No newline at end of file
diff --git a/src/build/expression/Expression.go b/src/build/expression/Expression.go
index 3a55506..55abb19 100644
--- a/src/build/expression/Expression.go
+++ b/src/build/expression/Expression.go
@@ -55,14 +55,16 @@ func (expr *Expression) Count(buffer []byte, kind token.Kind, name string) uint8
 
 // Reset resets all values to the default.
 func (expr *Expression) Reset() {
-	for _, child := range expr.Children {
-		child.Reset()
+	expr.Parent = nil
+
+	if expr.Children != nil {
+		expr.Children = expr.Children[:0]
 	}
 
 	expr.Token.Reset()
-	expr.Parent = nil
-	expr.Children = expr.Children[:0]
+	expr.Value = 0
 	expr.Precedence = 0
+	expr.IsFolded = false
 }
 
 // EachLeaf iterates through all leaves in the tree.
diff --git a/tests/examples_test.go b/tests/examples_test.go
index 94d5f80..0ff6142 100644
--- a/tests/examples_test.go
+++ b/tests/examples_test.go
@@ -22,6 +22,7 @@ var examples = []struct {
 	{"array", "", "Hello", 0},
 	{"echo", "Echo", "Echo", 0},
 	{"itoa", "", "9223372036854775807", 0},
+	{"collatz", "", "6 3 10 5 16 8 4 2 1", 0},
 }
 
 func TestExamples(t *testing.T) {