diff --git a/compiler/middle/lower_ast.ts b/compiler/middle/lower_ast.ts
index a87cfb9..632cb24 100644
--- a/compiler/middle/lower_ast.ts
+++ b/compiler/middle/lower_ast.ts
@@ -91,35 +91,3 @@ export class AstLowerer {
         return todo();
     }
 }
-
-// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/struct.Rib.html
-type Rib = {
-    kind: RibKind;
-    bindings: Map<IdentId, Res>;
-};
-
-// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/enum.RibKind.html
-type RibKind =
-    | { tag: "normal" }
-    | { tag: "fn" }
-    | { tag: "item"; defKind: DefKind }
-    | { tag: "mod" };
-
-// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/enum.RibKind.html
-type Res =
-    | { tag: "error" }
-    | { tag: "def"; kind: DefKind; id: DefId }
-    | { tag: "local"; id: DefId };
-
-// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def/enum.DefKind.html
-type DefKind =
-    | { type: "mod" }
-    | { type: "struct" }
-    | { type: "enum" }
-    | { type: "variant" }
-    | { type: "ty_alias" }
-    | { type: "ty_param" }
-    | { type: "fn" }
-    | { type: "ctor" }
-    | { type: "use" }
-    | { type: "field" };
diff --git a/compiler/middle/rib.ts b/compiler/middle/rib.ts
new file mode 100644
index 0000000..937e70a
--- /dev/null
+++ b/compiler/middle/rib.ts
@@ -0,0 +1,33 @@
+import { DefId, IdentId } from "../ctx.ts";
+
+// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/struct.Rib.html
+export type Rib = {
+    kind: RibKind;
+    bindings: Map<IdentId, Res>;
+};
+
+// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/enum.RibKind.html
+export type RibKind =
+    | { tag: "normal" }
+    | { tag: "fn" }
+    | { tag: "item"; defKind: DefKind }
+    | { tag: "mod" };
+
+// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/enum.RibKind.html
+export type Res =
+    | { tag: "error" }
+    | { tag: "def"; kind: DefKind; id: DefId }
+    | { tag: "local"; id: DefId };
+
+// https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def/enum.DefKind.html
+export type DefKind =
+    | { type: "mod" }
+    | { type: "struct" }
+    | { type: "enum" }
+    | { type: "variant" }
+    | { type: "ty_alias" }
+    | { type: "ty_param" }
+    | { type: "fn" }
+    | { type: "ctor" }
+    | { type: "use" }
+    | { type: "field" };