Working example

src/external/runtime_error.rs

@@ -0,0 +1,27 @@
+use std::{rc::Rc, fmt::Display};
+
+use crate::foreign::ExternError;
+
+#[derive(Clone)]
+pub struct RuntimeError {
+  message: String,
+  operation: &'static str,
+}
+
+impl RuntimeError {
+  pub fn fail(message: String, operation: &'static str) -> Result<!, Rc<dyn ExternError>> {
+    return Err(Self { message, operation }.into_extern())
+  }
+
+  pub fn ext(message: String, operation: &'static str) -> Rc<dyn ExternError> {
+    return Self { message, operation }.into_extern()
+  }
+}
+
+impl Display for RuntimeError {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "Error while {}: {}", self.operation, self.message)
+  }
+}
+
+impl ExternError for RuntimeError{}