Most files suffered major changes

- Less ambiguous syntax
- Better parser (Chumsky only does tokenization now)
- Tidy(|ier) error handling
- Facade for simplified embedding
- External code grouped in (fairly) self-contained Systems
- Dynamic action dispatch
- Many STL additions

src/error/too_many_supers.rs

@@ -0,0 +1,43 @@
+use std::rc::Rc;
+
+use super::{ErrorPosition, ProjectError};
+use crate::representations::location::Location;
+use crate::utils::iter::box_once;
+use crate::utils::BoxedIter;
+use crate::{Interner, VName};
+
+/// Error produced when an import path starts with more `super` segments
+/// than the current module's absolute path
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct TooManySupers {
+  /// The offending import path
+  pub path: VName,
+  /// The file containing the offending import
+  pub offender_file: VName,
+  /// The module containing the offending import
+  pub offender_mod: VName,
+}
+impl ProjectError for TooManySupers {
+  fn description(&self) -> &str {
+    "an import path starts with more `super` segments than the current \
+     module's absolute path"
+  }
+  fn message(&self, i: &Interner) -> String {
+    format!(
+      "path {} in {} contains too many `super` steps.",
+      i.extern_all(&self.path).join("::"),
+      i.extern_all(&self.offender_mod).join("::")
+    )
+  }
+
+  fn positions(&self, i: &Interner) -> BoxedIter<ErrorPosition> {
+    box_once(ErrorPosition {
+      location: Location::File(Rc::new(i.extern_all(&self.offender_file))),
+      message: Some(format!(
+        "path {} in {} contains too many `super` steps.",
+        i.extern_all(&self.path).join("::"),
+        i.extern_all(&self.offender_mod).join("::")
+      )),
+    })
+  }
+}