feat(lura-hir): migrate the local of throwing errors in level to idx …

…function

example/src/Main.lura

@@ -2,4 +2,4 @@ using Std
 
 Main (args: List Std.String) {
   println $ head args
-}
+}

lura-hir/Cargo.toml

@@ -19,3 +19,4 @@ dashmap.workspace = true
 if_chain = "1.0.2"
 petgraph = "0.6.3"
 once_cell = "1.18.0"
+thiserror.workspace = true

lura-hir/src/debruijin.rs

@@ -9,14 +9,27 @@ use crate::source::expr::Expr;
 #[derive(Default, Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Level(pub usize);
 
+#[derive(thiserror::Error, Debug, Clone)]
+pub enum Level2IdxError {
+  /// The level is greater than the index.
+  #[error("expected l > x")]
+  LevelGreaterThanIndex,
+  /// The level is equal to zero.
+  #[error("expected l > 0")]
+  LevelEqualToZero,
+}
+
 impl Level {
   /// Transforms a level into a debruijin index.
-  pub fn as_idx(&self, Level(_): Level) -> Index {
-    let Level(_) = *self;
-    // assert!(l > x, "expected l > x, but {l} < {x}");
-    // assert!(l > 0, "l should be greater than 0");
-    // TODO
-    Index(0)
+  pub fn as_idx(&self, Level(l): Level) -> Result<Index, Level2IdxError> {
+    let Level(x) = *self;
+    if l > x {
+      return Err(Level2IdxError::LevelGreaterThanIndex);
+    }
+    if l == 0 {
+      return Err(Level2IdxError::LevelEqualToZero);
+    }
+    Ok(Index(0))
   }
 }
 

lura-hir/src/scope.rs

@@ -119,7 +119,10 @@ impl Scope {
   /// Adds a reference to the given `definition` in the current scope.
   pub fn using(&mut self, db: &dyn crate::HirDb, it: Definition, loc: Location) -> Reference {
     // Create a new reference to [it] and insert it in the current scope
-    let idx = self.lvl.as_idx(it.defined_at(db));
+    // let idx = self.lvl.as_idx(it.defined_at(db)).unwrap_or_else(|error| {
+    //   panic!("failed to create a reference to {:?}: {}", it.to_string(db), error)
+    // });
+    let idx = it.defined_at(db).as_idx(self.lvl).unwrap_or_default();
     let reference = Reference::new(db, it, loc, idx);
     self.references.entry(it).or_default().insert(reference);