diff --git a/outrun-compiler/src/ir/context.rs b/outrun-compiler/src/ir/context.rs
index 3c67b56..5b90e67 100644
--- a/outrun-compiler/src/ir/context.rs
+++ b/outrun-compiler/src/ir/context.rs
@@ -1,13 +1,14 @@
 use super::{Error, Function, Notice, NoticeKind, NoticeLevel, Type, TypeVariable};
 use crate::source::Source;
 use crate::span::Span;
+use crate::unique_id::UniqueIdGenerator;
 use outrun_common::{Stack, StackError};
 use std::cell::RefCell;
 use std::sync::Arc;
 
 #[derive(Debug, Clone)]
 pub struct Context {
-    pub source: Arc<Source>,
+    pub source: Option<Arc<Source>>,
     pub types: Vec<Arc<Type>>,
     pub functions: Vec<Arc<Function>>,
     pub docs: Stack<String>,
@@ -15,24 +16,29 @@ pub struct Context {
     pub current_type: Stack<Arc<Type>>,
     pub self_type: Stack<Arc<Type>>,
     pub current_function: Stack<Arc<Function>>,
-    type_id: u64,
+    type_id: UniqueIdGenerator,
 }
 
 impl Context {
-    pub fn new(source: Arc<Source>) -> Context {
+    pub fn new() -> Context {
         bootstrap(Context {
-            source,
+            source: None,
             types: Vec::new(),
             functions: Vec::new(),
             docs: Stack::new(),
             notices: Vec::new(),
-            type_id: 0,
+            type_id: UniqueIdGenerator::new(),
             current_type: Stack::new(),
             self_type: Stack::new(),
             current_function: Stack::new(),
         })
     }
 
+    pub fn with_source(mut self, source: Arc<Source>) -> Self {
+        self.source = Some(source);
+        self
+    }
+
     pub fn find_named_type<T: ToString>(&self, name: T) -> Result<Arc<Type>, Error> {
         let name = name.to_string();
 
@@ -59,8 +65,7 @@ impl Context {
     }
 
     pub fn unbound_type(&mut self) -> Result<Arc<Type>, Error> {
-        let type_id = self.type_id;
-        self.type_id += 1;
+        let type_id = self.type_id.next();
         let r#type = RefCell::new(TypeVariable::Unbound { id: type_id });
         let r#type = Arc::new(Type::Variable { r#type, span: None });
         self.types.push(r#type.clone());
@@ -108,31 +113,47 @@ impl Context {
             .ok_or_else(|| StackError::Underflow.into())
     }
 
-    pub fn info(&mut self, span: Option<Span>, kind: NoticeKind) {
-        self.notices.push(Notice {
-            source: self.source.clone(),
+    pub fn info(&mut self, span: Option<Span>, kind: NoticeKind) -> Result<(), Error> {
+        let source = self.assert_has_source()?;
+
+        let notice = Notice {
+            source: source,
             level: NoticeLevel::Info,
             kind,
             span,
-        })
+        };
+
+        self.notices.push(notice);
+
+        Ok(())
     }
 
-    pub fn warning(&mut self, span: Option<Span>, kind: NoticeKind) {
-        self.notices.push(Notice {
-            source: self.source.clone(),
+    pub fn warning(&mut self, span: Option<Span>, kind: NoticeKind) -> Result<(), Error> {
+        let source = self.assert_has_source()?;
+
+        let notice = Notice {
+            source: source,
             level: NoticeLevel::Warning,
             kind,
             span,
-        })
+        };
+
+        self.notices.push(notice);
+        Ok(())
     }
 
-    pub fn error(&mut self, span: Option<Span>, kind: NoticeKind) {
-        self.notices.push(Notice {
-            source: self.source.clone(),
+    pub fn error(&mut self, span: Option<Span>, kind: NoticeKind) -> Result<(), Error> {
+        let source = self.assert_has_source()?;
+
+        let notice = Notice {
+            source: source,
             level: NoticeLevel::Error,
             kind,
             span,
-        })
+        };
+
+        self.notices.push(notice);
+        Ok(())
     }
 
     pub fn search_type<F>(&self, predicate: F) -> Option<Arc<Type>>
@@ -141,6 +162,17 @@ impl Context {
     {
         self.types.iter().find(|t| predicate((*t).clone())).cloned()
     }
+
+    fn assert_has_source(&self) -> Result<Arc<Source>, Error> {
+        if let Some(source) = self.source.as_ref() {
+            return Ok(source.clone());
+        }
+
+        Err(Error::InternalError(
+            "Attempt use context without source".to_string(),
+            None,
+        ))
+    }
 }
 
 fn bootstrap(mut module: Context) -> Context {
diff --git a/outrun-compiler/src/ir/error.rs b/outrun-compiler/src/ir/error.rs
index 941a81e..c9707e8 100644
--- a/outrun-compiler/src/ir/error.rs
+++ b/outrun-compiler/src/ir/error.rs
@@ -24,6 +24,8 @@ pub enum Error {
     },
     #[error("{0}")]
     Stack(#[from] StackError),
+    #[error("Internal compiler error: {0}")]
+    InternalError(String, Option<Span>),
 }
 
 impl Error {
@@ -33,6 +35,7 @@ impl Error {
             Error::UnknownType(_) => None,
             Error::MissingProperty { span, .. } => Some(*span),
             Error::Stack(_) => None,
+            Error::InternalError(_, span) => *span,
         }
     }
 }
diff --git a/outrun-compiler/src/ir/stages.rs b/outrun-compiler/src/ir/stages.rs
index ba7d8c9..7198135 100644
--- a/outrun-compiler/src/ir/stages.rs
+++ b/outrun-compiler/src/ir/stages.rs
@@ -17,7 +17,7 @@ pub fn link_type_references(mut context: Context) -> Result<Context, Error> {
         if let Some(target) = maybe_type {
             ty.link_to(target);
         } else {
-            context.error(ty.span(), NoticeKind::CannotResolveType(target_name));
+            context.error(ty.span(), NoticeKind::CannotResolveType(target_name))?;
         }
     }
 
diff --git a/outrun-compiler/src/ir/visitor.rs b/outrun-compiler/src/ir/visitor.rs
index 1e745f6..fe11e9a 100644
--- a/outrun-compiler/src/ir/visitor.rs
+++ b/outrun-compiler/src/ir/visitor.rs
@@ -81,7 +81,7 @@ fn eval_type_union(mut context: Context, node: Node) -> Result<(Context, Arc<Typ
             } else if name.starts_with("Self.") {
                 let (mut context, parent) = self_type(context)?;
                 if parent.is_named() {
-                    let name = parent.to_string();
+                    let name = name.replace("Self", &parent.to_string());
                     let ty = context.reference_type(name, Some(node.span))?;
                     Ok((context, ty))
                 } else {
@@ -236,7 +236,7 @@ fn visit_atom(mut context: Context, node: Node) -> Result<(Context, Expression),
         context.info(
             Some(node.span),
             NoticeKind::UnconventionalAtom(value.clone(), suggestion),
-        )
+        )?;
     }
 
     let value = ExpressionValue::Atom(value);
@@ -347,7 +347,7 @@ fn visit_function_statement(mut context: Context, node: Node) -> Result<Context,
                 context.info(
                     Some(node.span),
                     NoticeKind::UnconventionalFunctionName(name.clone(), suggestion),
-                );
+                )?;
             }
 
             let associated_type = context.current_type.peek().cloned()?;
@@ -361,7 +361,7 @@ fn visit_function_statement(mut context: Context, node: Node) -> Result<Context,
                     context.info(
                         Some(node.span),
                         NoticeKind::UnconventionalKeyword(key.clone(), suggestion),
-                    );
+                    )?;
                 }
 
                 argument_names.push(key);
@@ -447,7 +447,7 @@ fn visit_function_statement(mut context: Context, node: Node) -> Result<Context,
                 context.warning(
                     Some(span),
                     NoticeKind::UnexpectedFunctionProperty(key.to_string()),
-                );
+                )?;
             }
 
             Ok(context)
@@ -467,7 +467,7 @@ fn visit_get_local(mut context: Context, node: Node) -> Result<(Context, Express
                 context.info(
                     Some(span),
                     NoticeKind::UnconventionalVariableName(local.clone(), suggestion),
-                )
+                )?;
             }
 
             let r#type = context.unbound_type()?;
@@ -534,7 +534,7 @@ fn visit_impl(mut context: Context, node: Node) -> Result<(Context, Arc<Type>),
                 context.warning(
                     Some(node.span),
                     NoticeKind::UnexpectedImplProperty(key.to_string()),
-                );
+                )?;
             }
 
             Ok((context, ty))
@@ -556,7 +556,7 @@ fn visit_index(context: Context, node: Node) -> Result<(Context, Expression), Er
                 context.info(
                     Some(node.span),
                     NoticeKind::UnconventionalFieldName(field_name.clone(), suggestion),
-                );
+                )?;
             }
 
             let value = ExpressionValue::Index {
@@ -644,7 +644,7 @@ fn visit_let_expression(mut context: Context, node: Node) -> Result<(Context, Ex
                 context.info(
                     Some(span),
                     NoticeKind::UnconventionalVariableName(name.clone(), suggestion),
-                );
+                )?;
             }
 
             let expression_type;
@@ -792,7 +792,7 @@ fn visit_protocol(mut context: Context, node: Node) -> Result<(Context, Arc<Type
                 context.warning(
                     Some(node.span),
                     NoticeKind::UnexpectedProtocolProperty(key.to_string()),
-                );
+                )?;
             }
 
             Ok((context, ty))
@@ -882,7 +882,7 @@ fn visit_struct(mut context: Context, node: Node) -> Result<(Context, Arc<Type>)
                     context.info(
                         Some(node.span),
                         NoticeKind::UnconventionalFieldName(key.clone(), suggestion),
-                    );
+                    )?;
                 }
 
                 let (new_context, value) = eval_type_union(context, value.clone())?;
@@ -921,7 +921,7 @@ fn visit_struct(mut context: Context, node: Node) -> Result<(Context, Arc<Type>)
                 context.warning(
                     Some(node.span),
                     NoticeKind::UnexpectedStructProperty(key.to_string()),
-                );
+                )?;
             }
 
             Ok((context, r#type))
@@ -988,7 +988,7 @@ fn visit_use_statement(mut context: Context, node: Node) -> Result<Context, Erro
                 context.warning(
                     Some(node.span),
                     NoticeKind::UnexpectedUseProperty(key.to_string()),
-                );
+                )?;
             }
 
             if let Some(alias) = props.get("as") {
@@ -1013,7 +1013,7 @@ fn typename_to_string(context: &mut Context, node: &Node) -> Result<String, Erro
                 context.info(
                     Some(node.span),
                     NoticeKind::UnconventionalTypeName(value.clone(), suggestion),
-                );
+                )?;
             }
 
             Ok(value)
diff --git a/outrun-compiler/src/lib.rs b/outrun-compiler/src/lib.rs
index 5019c0b..9c23783 100644
--- a/outrun-compiler/src/lib.rs
+++ b/outrun-compiler/src/lib.rs
@@ -19,6 +19,7 @@ mod grammar;
 mod ir;
 mod source;
 mod span;
+mod unique_id;
 
 use std::sync::Arc;
 
@@ -27,10 +28,10 @@ pub use ir::Context;
 pub use ir::Type;
 pub use source::Source;
 
-pub fn compile(source: Arc<Source>) -> Result<Context, Error> {
+pub fn compile(context: Context, source: Arc<Source>) -> Result<Context, Error> {
     let ast = grammar::parse(source.clone(), None).map_err(|e| (source.clone(), e))?;
 
-    let context = Context::new(source.clone());
+    let context = context.with_source(source.clone());
     let context = ir::visit_nodes(context, ast).map_err(|e| (source.clone(), e))?;
     let context = ir::improve(context).map_err(|e| (source.clone(), e))?;
 
diff --git a/outrun-compiler/src/unique_id.rs b/outrun-compiler/src/unique_id.rs
new file mode 100644
index 0000000..946a253
--- /dev/null
+++ b/outrun-compiler/src/unique_id.rs
@@ -0,0 +1,53 @@
+use std::sync::{
+    atomic::{AtomicU64, Ordering},
+    Arc,
+};
+
+/// A unique identifier generator.
+///
+/// Blatantly stolen from https://github.com/gleam-lang/gleam/blob/main/compiler-core/src/uid.rs
+
+/// A generator of unique ids. Only one should be used per compilation run to
+/// ensure ids do not get reused.
+#[derive(Debug, Clone, Default)]
+pub struct UniqueIdGenerator {
+    id: Arc<AtomicU64>,
+}
+
+impl UniqueIdGenerator {
+    /// Fork the id generator into a new one that does not share the same
+    /// internal id. It will increment independently. Not to be used in the same
+    /// compilation run.
+    pub fn fork(&self) -> Self {
+        let current = self.id.load(Ordering::Relaxed);
+        let id = AtomicU64::new(current);
+        Self { id: Arc::new(id) }
+    }
+
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn next(&self) -> u64 {
+        self.id.fetch_add(1, Ordering::Relaxed)
+    }
+}
+
+#[test]
+fn id_generation() {
+    let ids = UniqueIdGenerator::new();
+    let ids2 = ids.clone();
+
+    assert_eq!(ids.next(), 0);
+    assert_eq!(ids.next(), 1);
+    assert_eq!(ids.next(), 2);
+
+    // Cloned ones use the same counter
+    assert_eq!(ids2.next(), 3);
+    assert_eq!(ids2.next(), 4);
+    assert_eq!(ids2.next(), 5);
+
+    // The original is updated
+    assert_eq!(ids.next(), 6);
+    assert_eq!(ids.next(), 7);
+}
diff --git a/outrun-core/src/lib.rs b/outrun-core/src/lib.rs
index 1f35e08..59a947e 100644
--- a/outrun-core/src/lib.rs
+++ b/outrun-core/src/lib.rs
@@ -6,23 +6,22 @@ use std::fs;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-pub fn init() -> Result<Vec<Context>, Error> {
+pub fn init() -> Result<Context, Error> {
     let path = Path::new(env!("CARGO_MANIFEST_DIR"));
     let path = path.join("lib");
     let path = path.as_path();
 
     let files = collect_files(path, Vec::new())?;
 
-    let mut results = Vec::new();
+    let mut context = Context::new();
 
     for path in files.iter().take(1) {
         let source = Source::from_file(path)?;
         let source = Arc::new(source);
-        let context = outrun_compiler::compile(source)?;
-        results.push(context);
+        context = outrun_compiler::compile(context, source)?;
     }
 
-    Ok(results)
+    Ok(context)
 }
 
 fn collect_files(path: &Path, mut files: Vec<PathBuf>) -> Result<Vec<PathBuf>, Error> {
@@ -52,21 +51,19 @@ mod test {
 
     #[test]
     fn test_init() -> Result<()> {
-        let results = init()?;
+        let context = init()?;
 
         // println!("results: {:#?}", results);
 
-        for context in results {
-            let unbound_types: Vec<Arc<Type>> = context
-                .types
-                .iter()
-                .filter(|t| t.is_unbound())
-                .cloned()
-                .collect();
-            println!("unbound_types: {:#?}", unbound_types);
+        let unbound_types: Vec<Arc<Type>> = context
+            .types
+            .iter()
+            .filter(|t| t.is_unbound())
+            .cloned()
+            .collect();
+        println!("unbound_types: {:#?}", unbound_types);
 
-            assert_eq!(unbound_types.len(), 0);
-        }
+        assert_eq!(unbound_types.len(), 0);
 
         Ok(())
     }