make runtime errors std::error::Error

1 files changed, 8 insertions, 0 deletions

diff --git a/src/forth/vm.rs b/src/forth/vm.rs
index a4f57c7..e4c01f2 100644
--- a/src/forth/vm.rs
+++ b/src/forth/vm.rs
@@ -114,6 +114,14 @@ pub struct VM {
 pub enum RuntimeError {
     StackUnderflow,
 }
+impl std::fmt::Display for RuntimeError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::StackUnderflow => write!(f, "stack underflow"),
+        }
+    }
+}
+impl std::error::Error for RuntimeError {}
 
 impl VM {
     pub fn new(wordlist: WordList) -> Self {