3 files changed, 28 insertions, 8 deletions
diff --git a/src/compiler.rs b/src/compiler.rs
index c0dacec..c70640d 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -923,8 +923,7 @@ impl Compiler {
                 };
                 add_op(self, block, Op::Link(slot));
                 if let Value::Function(_, block) = &self.constants[slot] {
-                    let needs_linking = block.borrow().upvalues.len() != 0;
-                    block.borrow_mut().constant = needs_linking;
+                    block.borrow_mut().mark_constant();
                 } else {
                     unreachable!();
                 }
diff --git a/src/lib.rs b/src/lib.rs
index 1bdcc00..42a74a0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -626,17 +626,23 @@ mod op {
 }
 
 #[derive(Debug)]
+enum BlockLinkState {
+    Linked,
+    Unlinked,
+    Nothing,
+}
+
+#[derive(Debug)]
 pub struct Block {
     pub ty: Type,
     upvalues: Vec<(usize, bool, Type)>,
+    linking: BlockLinkState,
 
     pub name: String,
     pub file: PathBuf,
     ops: Vec<Op>,
     last_line_offset: usize,
     line_offsets: HashMap<usize, usize>,
-    linked: bool,
-    constant: bool,
 }
 
 impl Block {
@@ -644,16 +650,31 @@ impl Block {
         Self {
             ty: Type::Void,
             upvalues: Vec::new(),
+            linking: BlockLinkState::Nothing,
+
             name: String::from(name),
             file: file.to_owned(),
             ops: Vec::new(),
             last_line_offset: 0,
             line_offsets: HashMap::new(),
-            linked: false,
-            constant: false,
         }
     }
 
+    fn mark_constant(&mut self) {
+        if self.upvalues.is_empty() {
+            return;
+        }
+        self.linking = BlockLinkState::Unlinked;
+    }
+
+    fn link(&mut self) {
+        self.linking = BlockLinkState::Linked;
+    }
+
+    fn needs_linking(&self) -> bool {
+        matches!(self.linking, BlockLinkState::Unlinked)
+    }
+
     // Used to create empty functions.
     fn stubbed_block(ty: &Type) -> Self {
         let mut block = Block::new("/empty/", Path::new(""));
diff --git a/src/vm.rs b/src/vm.rs
index 20125be..5e7810d 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -557,7 +557,7 @@ impl VM {
                     Value::Function(_, block) => {
                         self.push(Value::Function(Vec::new(), block.clone()));
 
-                        if block.borrow().constant && !block.borrow().linked {
+                        if block.borrow().needs_linking() {
                             error!(self,
                                 ErrorKind::InvalidProgram,
                                 format!("Calling function '{}' before all captured variables are declared.",
@@ -676,7 +676,7 @@ impl VM {
             Op::Link(slot) => {
                 match self.constant(slot).clone() {
                     Value::Function(_, block) => {
-                        block.borrow_mut().linked = true;
+                        block.borrow_mut().link();
                     }
                     value => {
                         error!(self,