More work on resolution

crates/frontend/src/resolve.rs

@@ -74,7 +74,7 @@ pub fn rule<'db>(db: &'db dyn Database, ast: ast::Rule<'db>) -> Rule<'db> {
         // if a body is present, resolve separately
         Some(body) => rule_body(db, body),
 
-        // if a body is absent, create an explicit rule body by hand
+        // if a body is absent, create an implicit rule body by hand
         None => RuleBody {
             meta: ast.ast(db),
             vars: Default::default(),
@@ -86,7 +86,7 @@ pub fn rule<'db>(db: &'db dyn Database, ast: ast::Rule<'db>) -> Rule<'db> {
         },
     };
 
-    // the head is empty for now because it is untyped
+    // the head is empty for now because types are unknown
     let head = Default::default();
 
     // resolve the name of the target relation
@@ -104,7 +104,15 @@ pub fn rule<'db>(db: &'db dyn Database, ast: ast::Rule<'db>) -> Rule<'db> {
 /// Resolves all references in an [ast::Assumption].
 #[salsa::tracked]
 pub fn assumption<'db>(db: &'db dyn Database, ast: ast::Assumption<'db>) -> Assumption<'db> {
-    todo!()
+    // resolve the body
+    let body = rule_body(db, ast.body(db));
+
+    // assemble the completed assumption
+    Assumption {
+        meta: ast,
+        weight: todo!(),
+        body,
+    }
 }
 
 /// Resolves all references in an [ast::RuleBody].
@@ -192,7 +200,11 @@ pub fn expr<'db>(
                 Variable(vars.insert_full(VariableMeta::Named(name.clone())).0)
             }
 
-            ast::ExprExtra::Apply(apply) => todo!(),
+            // application resolves the head and recursively resolves the body
+            ast::ExprExtra::Apply(apply) => Extra(Arc::new(ExprExtra::Apply(Apply {
+                body: resolve(&apply.body),
+                relation: loaded.insert_full(relation_name(db, apply.head.clone())).0,
+            }))),
 
             ast::ExprExtra::Aggregate(aggregate) => todo!(),
         },
@@ -241,7 +253,7 @@ impl<'db> ir::ProgramInfo for ProgramInfo<'db> {
     /// [RelationLabel] fallibly identifies relations after the resolution stage.
     type RelationLabel = RelationLabel<'db>;
 
-    type AssumptionMeta = Infallible;
+    type AssumptionMeta = ast::Assumption<'db>;
 
     type RuleMeta = ast::Rule<'db>;
 
@@ -301,7 +313,7 @@ pub enum VariableMeta {
     Hole(AstNode),
 }
 
-/// A high-level application operation.
+/// A high-level, resolved application operation.
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub struct Apply<'db> {
     /// The source relation's index in the parent [RuleBody].