diff --git a/crates/rue-compiler/src/error.rs b/crates/rue-compiler/src/error.rs
index 1cd3943..77706e3 100644
--- a/crates/rue-compiler/src/error.rs
+++ b/crates/rue-compiler/src/error.rs
@@ -38,14 +38,23 @@ pub enum DiagnosticKind {
 
 #[derive(Debug, Error, Clone, PartialEq, Eq, Hash)]
 pub enum WarningKind {
-    #[error("redundant optional type")]
-    RedundantOptional,
+    #[error("marking optional types as optional again has no effect")]
+    UselessOptional,
 
-    #[error("redundant check against same type `{0}`")]
+    #[error("redundant type check against `{0}`, value is already that type")]
     RedundantTypeGuard(String),
 
-    #[error("unused symbol `{0}`")]
-    UnusedSymbol(String),
+    #[error("unused function `{0}`")]
+    UnusedFunction(String),
+
+    #[error("unused parameter `{0}`")]
+    UnusedParameter(String),
+
+    #[error("unused constant `{0}`")]
+    UnusedConst(String),
+
+    #[error("unused let binding `{0}`")]
+    UnusedLet(String),
 
     #[error("unused type `{0}`")]
     UnusedType(String),
diff --git a/crates/rue-compiler/src/lib.rs b/crates/rue-compiler/src/lib.rs
index 9c41413..45f477b 100644
--- a/crates/rue-compiler/src/lib.rs
+++ b/crates/rue-compiler/src/lib.rs
@@ -1,3 +1,5 @@
+#![warn(clippy::needless_pass_by_ref_mut)]
+
 use clvmr::{Allocator, NodePtr};
 use codegen::Codegen;
 use lowerer::Lowerer;
diff --git a/crates/rue-compiler/src/lowerer.rs b/crates/rue-compiler/src/lowerer.rs
index a8ce557..e332492 100644
--- a/crates/rue-compiler/src/lowerer.rs
+++ b/crates/rue-compiler/src/lowerer.rs
@@ -1922,10 +1922,7 @@ impl<'a> Lowerer<'a> {
             .unwrap_or(self.unknown_type);
 
         if let Type::Optional(inner) = self.db.ty_raw(ty).clone() {
-            self.warning(
-                WarningKind::RedundantOptional,
-                optional.syntax().text_range(),
-            );
+            self.warning(WarningKind::UselessOptional, optional.syntax().text_range());
             return inner;
         }
 
diff --git a/crates/rue-compiler/src/optimizer.rs b/crates/rue-compiler/src/optimizer.rs
index 4c36d4b..5ebca2d 100644
--- a/crates/rue-compiler/src/optimizer.rs
+++ b/crates/rue-compiler/src/optimizer.rs
@@ -91,37 +91,49 @@ impl<'a> Optimizer<'a> {
         }
     }
 
-    fn compute_captures_entrypoint(
+    fn check_unused(
         &mut self,
         scope_id: ScopeId,
-        inherits_from: Option<ScopeId>,
-        hir_id: HirId,
+        used_symbols: HashSet<SymbolId>,
+        used_types: HashSet<TypeId>,
     ) {
-        if self.environments.contains_key(&scope_id) {
-            return;
-        }
-
-        self.environments.insert(scope_id, Environment::default());
-        let used_types = self.db.scope(scope_id).used_types().clone();
-        self.env_mut(scope_id).used_types.extend(used_types);
-        self.env_mut(scope_id).inherits_from = inherits_from;
-        self.compute_captures_hir(scope_id, hir_id);
-
         let unused_symbols: Vec<SymbolId> = self
             .db
             .scope(scope_id)
             .local_symbols()
             .iter()
-            .filter(|&symbol_id| !self.env(scope_id).used_symbols.contains(symbol_id))
+            .filter(|&symbol_id| !used_symbols.contains(symbol_id))
             .copied()
             .collect();
 
         for symbol_id in unused_symbols {
             if let Some(token) = self.db.symbol_token(symbol_id) {
-                self.warning(
-                    WarningKind::UnusedSymbol(token.to_string()),
-                    token.text_range(),
-                );
+                match self.db.symbol(symbol_id).clone() {
+                    Symbol::Function { .. } => {
+                        self.warning(
+                            WarningKind::UnusedFunction(token.to_string()),
+                            token.text_range(),
+                        );
+                    }
+                    Symbol::Parameter { .. } => {
+                        self.warning(
+                            WarningKind::UnusedParameter(token.to_string()),
+                            token.text_range(),
+                        );
+                    }
+                    Symbol::LetBinding { .. } => {
+                        self.warning(
+                            WarningKind::UnusedLet(token.to_string()),
+                            token.text_range(),
+                        );
+                    }
+                    Symbol::ConstBinding { .. } => {
+                        self.warning(
+                            WarningKind::UnusedConst(token.to_string()),
+                            token.text_range(),
+                        );
+                    }
+                }
             }
         }
 
@@ -130,7 +142,7 @@ impl<'a> Optimizer<'a> {
             .scope(scope_id)
             .local_types()
             .iter()
-            .filter(|&type_id| !self.env(scope_id).used_types.contains(type_id))
+            .filter(|&type_id| !used_types.contains(type_id))
             .copied()
             .collect();
 
@@ -144,6 +156,29 @@ impl<'a> Optimizer<'a> {
         }
     }
 
+    fn compute_captures_entrypoint(
+        &mut self,
+        scope_id: ScopeId,
+        inherits_from: Option<ScopeId>,
+        hir_id: HirId,
+    ) {
+        if self.environments.contains_key(&scope_id) {
+            return;
+        }
+
+        self.environments.insert(scope_id, Environment::default());
+        let used_types = self.db.scope(scope_id).used_types().clone();
+        self.env_mut(scope_id).used_types.extend(used_types);
+        self.env_mut(scope_id).inherits_from = inherits_from;
+        self.compute_captures_hir(scope_id, hir_id);
+
+        self.check_unused(
+            scope_id,
+            self.env(scope_id).used_symbols.clone(),
+            self.env(scope_id).used_types.clone(),
+        );
+    }
+
     fn compute_captures_hir(&mut self, scope_id: ScopeId, hir_id: HirId) {
         match self.db.hir(hir_id).clone() {
             Hir::Unknown | Hir::Atom(_) => {}
@@ -240,46 +275,13 @@ impl<'a> Optimizer<'a> {
 
         self.compute_captures_entrypoint(scope_id, None, hir_id);
 
-        let unused_symbols: Vec<SymbolId> = self
-            .db
-            .scope(root_scope_id)
-            .local_symbols()
-            .iter()
-            .filter(|&symbol_id| {
-                !self.env(scope_id).used_symbols.contains(symbol_id) && *symbol_id != main
-            })
-            .copied()
-            .collect();
+        let mut used_symbols = self.env(scope_id).used_symbols.clone();
+        used_symbols.insert(main);
 
-        for symbol_id in unused_symbols {
-            if let Some(token) = self.db.symbol_token(symbol_id) {
-                self.warning(
-                    WarningKind::UnusedSymbol(token.to_string()),
-                    token.text_range(),
-                );
-            }
-        }
-
-        let unused_types: Vec<TypeId> = self
-            .db
-            .scope(root_scope_id)
-            .local_types()
-            .iter()
-            .filter(|&type_id| {
-                !self.env(scope_id).used_types.contains(type_id)
-                    && !self.db.scope(root_scope_id).used_types().contains(type_id)
-            })
-            .copied()
-            .collect();
+        let mut used_types = self.env(scope_id).used_types.clone();
+        used_types.extend(self.db.scope(root_scope_id).used_types().clone());
 
-        for type_id in unused_types {
-            if let Some(token) = self.db.type_token(type_id) {
-                self.warning(
-                    WarningKind::UnusedType(token.to_string()),
-                    token.text_range(),
-                );
-            }
-        }
+        self.check_unused(root_scope_id, used_symbols, used_types);
 
         for symbol_id in self.db.scope(scope_id).local_symbols() {
             if self.db.symbol(symbol_id).is_parameter() {
diff --git a/tests.toml b/tests.toml
index c9ab9f9..53f598f 100644
--- a/tests.toml
+++ b/tests.toml
@@ -1,8 +1,8 @@
 [list_types]
 parser_errors = []
 compiler_errors = [
-    "unused symbol `empty_hinted` at 3:9",
-    "unused symbol `empty` at 2:9",
+    "unused let binding `empty_hinted` at 3:9",
+    "unused let binding `empty` at 2:9",
 ]
 
 [pair_types]