Dead end with macros

src/external/assertion_error.rs

@@ -0,0 +1,30 @@
+use std::rc::Rc;
+use std::fmt::Display;
+
+use crate::foreign::ExternError;
+use crate::representations::interpreted::Clause;
+
+
+#[derive(Clone)]
+pub struct AssertionError{
+  pub value: Clause,
+  pub assertion: &'static str,
+}
+
+impl AssertionError {
+  pub fn fail(value: Clause, assertion: &'static str) -> Result<!, Rc<dyn ExternError>> {
+    return Err(Self { value, assertion }.into_extern())
+  }
+
+  pub fn into_extern(self) -> Rc<dyn ExternError> {
+    Rc::new(self)
+  }
+}
+
+impl Display for AssertionError {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "Error: {:?} is not {}", self.value, self.assertion)
+  }
+}
+
+impl ExternError for AssertionError{}