3 files changed, 12 insertions, 0 deletions
diff --git a/exercises/15_traits/traits2.rs b/exercises/15_traits/traits2.rs
index 9a2bc07..18ebcb0 100644
--- a/exercises/15_traits/traits2.rs
+++ b/exercises/15_traits/traits2.rs
@@ -14,6 +14,10 @@ trait AppendBar {
 
 // TODO: Implement trait `AppendBar` for a vector of strings.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/exercises/15_traits/traits3.rs b/exercises/15_traits/traits3.rs
index 357f1d7..8412afa 100644
--- a/exercises/15_traits/traits3.rs
+++ b/exercises/15_traits/traits3.rs
@@ -23,6 +23,10 @@ struct OtherSoftware {
 impl Licensed for SomeSoftware {} // Don't edit this line
 impl Licensed for OtherSoftware {} // Don't edit this line
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/exercises/15_traits/traits4.rs b/exercises/15_traits/traits4.rs
index 7242c48..18db0d6 100644
--- a/exercises/15_traits/traits4.rs
+++ b/exercises/15_traits/traits4.rs
@@ -25,6 +25,10 @@ fn compare_license_types(software: ??, software_two: ??) -> bool {
     software.licensing_info() == software_two.licensing_info()
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;