diff --git a/crates/frontend/src/ast.rs b/crates/frontend/src/ast.rs
index 4066d1e..b677117 100644
--- a/crates/frontend/src/ast.rs
+++ b/crates/frontend/src/ast.rs
@@ -17,13 +17,50 @@
 use std::{convert::Infallible, fmt::Display, str::FromStr, sync::Arc};
 
 use ir::EnumParse;
-use strum::EnumIter;
+use strum::{EnumDiscriminants, EnumIter};
 
 use crate::prelude::*;
 
 // TODO: migrate AST logic (after redesigning grammar)
 // TODO: AST unit tests? executing on examples may be sufficient
 
+/// Retrieves, but does not parse, all top-level items in a file.
+// TODO: is `Vec` the most efficient to incrementally update here?
+#[salsa::tracked]
+pub fn items<'db>(db: &'db dyn Database, file: workspace::File) -> Vec<ItemMeta<'db>> {
+    todo!()
+}
+
+/// Parses an [ItemMeta] into its corresponding [Item].
+pub fn item<'db>(db: &'db dyn Database, meta: ItemMeta<'db>) -> WithAst<Item<'db>> {
+    todo!()
+}
+
+/// Common information on top-level items.
+#[salsa::tracked]
+pub struct ItemMeta<'db> {
+    /// Documentation comments on this item.
+    pub docs: Vec<AstNode>,
+
+    /// The AST node of the item itself.
+    pub ast: AstNode,
+
+    /// The kind of item this is.
+    pub kind: ItemKind,
+}
+
+/// The contents of a top-level item.
+#[derive(EnumDiscriminants)]
+#[strum_discriminants(name(ItemKind))]
+#[strum_discriminants(derive(Hash))]
+pub enum Item<'db> {
+    TypeAlias(TypeAlias<'db>),
+    Import,
+    Relation(Relation<'db>),
+    Rule,
+    Assumption,
+}
+
 /// Parse an expression from the AST.
 #[salsa::tracked]
 pub fn expr(db: &dyn Database, ast: AstNode) -> Expr {
@@ -32,12 +69,12 @@ pub fn expr(db: &dyn Database, ast: AstNode) -> Expr {
     // parse the kind depending on which field is selected
     let kind = if let Some(tuple) = ast.get_field(db, "tuple") {
         let els = tuple.get_fields(db, "el").map(|el| expr(db, el)).collect();
-        ExprKind::Extra(ExprExtra::Tuple(els))
+        ExprKind::Extra(Arc::new(ExprExtra::Tuple(els)))
     } else if let Some(val) = ast.get_field(db, "value") {
-        ExprKind::Value(parse_value(db, val))
+        ExprKind::Value(value(db, val))
     } else if let Some(var) = ast.get_field(db, "variable") {
         let name = var.contents(db).to_string();
-        ExprKind::Extra(ExprExtra::VariableName(name))
+        ExprKind::Extra(Arc::new(ExprExtra::VariableName(name)))
     } else if let Some(binary) = ast.get_field(db, "binary") {
         let op = binary.expect_field(db, "op").expect_parse(db);
         let lhs = Arc::new(expr(db, binary.expect_field(db, "lhs")));
@@ -51,7 +88,7 @@ pub fn expr(db: &dyn Database, ast: AstNode) -> Expr {
         let head = atom.expect_field(db, "head");
         let head = WithAst::new(head, head.contents(db).to_string());
         let body = expr(db, atom.expect_field(db, "body"));
-        ExprKind::Extra(ExprExtra::Atom { head, body })
+        ExprKind::Extra(Arc::new(ExprExtra::Atom { head, body }))
     } else if let Some(parens) = ast.get_field(db, "parens") {
         return expr(db, parens);
     } else {
@@ -62,6 +99,27 @@ pub fn expr(db: &dyn Database, ast: AstNode) -> Expr {
     Expr { meta: ast, kind }
 }
 
+/// Parses a value from an AST.
+fn value(db: &dyn Database, ast: AstNode) -> ir::Value {
+    use ir::Value::*;
+    if ast.get_field(db, "true").is_some() {
+        Boolean(true)
+    } else if ast.get_field(db, "false").is_some() {
+        Boolean(false)
+    } else if let Some(sym) = ast.get_field(db, "symbol") {
+        todo!()
+    } else {
+        let int = ast.expect_field(db, "integer");
+        match int.contents(db).to_string().parse() {
+            Ok(val) => Integer(val),
+            Err(_) => {
+                diagnostic::SimpleError::new(int, "failed to parse integer literal").accumulate(db);
+                Integer(0)
+            }
+        }
+    }
+}
+
 /// A type alias for parse stage [Expr].
 pub type Expr = ir::Expr<AstProgramInfo>;
 
@@ -77,7 +135,7 @@ impl ir::ProgramInfo for AstProgramInfo {
     type ExprMeta = AstNode;
     type BinaryOp = BinaryOpKind;
     type UnaryOp = ir::UnaryOpKind;
-    type ExprExtra = ExprExtra;
+    type ExprExtra = Arc<ExprExtra>;
 }
 
 /// Extra [ExprKind] variants in the parse stage.