diff --git a/cl-ast/src/lib.rs b/cl-ast/src/lib.rs
index 0824635..c333f40 100644
--- a/cl-ast/src/lib.rs
+++ b/cl-ast/src/lib.rs
@@ -37,7 +37,7 @@ pub struct File {
 }
 
 // Metadata decorators
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub struct Attrs {
     pub meta: Vec<Meta>,
 }
diff --git a/cl-repl/Cargo.toml b/cl-repl/Cargo.toml
index 9cc11d3..e8caf3f 100644
--- a/cl-repl/Cargo.toml
+++ b/cl-repl/Cargo.toml
@@ -20,3 +20,4 @@ argh = "0.1.12"
 
 [dev-dependencies]
 cl-structures = { path = "../cl-structures" }
+cl-typeck = { path = "../cl-typeck" }
diff --git a/cl-repl/examples/typeck.rs b/cl-repl/examples/typeck.rs
new file mode 100644
index 0000000..3302886
--- /dev/null
+++ b/cl-repl/examples/typeck.rs
@@ -0,0 +1,109 @@
+use cl_lexer::Lexer;
+use cl_parser::Parser;
+use cl_repl::repline::{error::Error as RlError, Repline};
+use cl_typeck::{name_collector::NameCollector, project::Project};
+use std::error::Error;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let mut prj = Project::default();
+    let mut tcol = NameCollector::new(&mut prj);
+
+    println!(
+        "--- {} v{} 💪🦈 ---",
+        env!("CARGO_BIN_NAME"),
+        env!("CARGO_PKG_VERSION"),
+    );
+
+    read_and(
+        "\x1b[33m",
+        "cl>",
+        "? >",
+        |line| -> Result<_, Box<dyn Error>> {
+            if line.trim_start().is_empty() {
+                query(&tcol)?;
+                return Ok(Response::Deny);
+            }
+            let mut parser = Parser::new(Lexer::new(line));
+            let code = match parser.file() {
+                Ok(code) => code,
+                Err(e) => Err(e)?,
+            };
+            tcol.file(&code)?;
+            Ok(Response::Accept)
+        },
+    )
+}
+
+pub enum Response {
+    Accept,
+    Deny,
+    Break,
+}
+
+fn read_and(
+    color: &str,
+    begin: &str,
+    again: &str,
+    mut f: impl FnMut(&str) -> Result<Response, Box<dyn Error>>,
+) -> Result<(), Box<dyn Error>> {
+    let mut rl = Repline::new(color, begin, again);
+    loop {
+        let line = match rl.read() {
+            Err(RlError::CtrlC(_)) => break,
+            Err(RlError::CtrlD(line)) => {
+                rl.deny();
+                line
+            }
+            Ok(line) => line,
+            Err(e) => Err(e)?,
+        };
+        print!("\x1b[G\x1b[J");
+        match f(&line) {
+            Ok(Response::Accept) => rl.accept(),
+            Ok(Response::Deny) => rl.deny(),
+            Ok(Response::Break) => break,
+            Err(e) => print!("\x1b[40G\x1bJ\x1b[91m{e}\x1b[0m"),
+        }
+    }
+    Ok(())
+}
+
+fn query(prj: &Project) -> Result<(), Box<dyn Error>> {
+    use cl_typeck::{
+        definition::{Def, DefKind},
+        type_kind::TypeKind,
+    };
+    read_and("\x1b[35m", "qy>", "? >", |line| {
+        if line.trim_start().is_empty() {
+            return Ok(Response::Break);
+        }
+        match line {
+            "$all\n" => println!("{prj:#?}"),
+            _ => {
+                // parse it as a path, and convert the path into a borrowed path
+                let path = Parser::new(Lexer::new(line)).path()?;
+
+                let Some((type_id, path)) = prj.get_type((&path).into(), prj.module_root) else {
+                    return Ok(Response::Deny);
+                };
+                let Def { name, vis, meta: _, kind, source: _, module } = &prj[type_id];
+                match (kind, prj.get_value(path, type_id)) {
+                    (_, Some((val, path))) => {
+                        println!("value {}; {path}\n{:#?}", usize::from(val), prj[val])
+                    }
+                    (DefKind::Type(TypeKind::Module), None) => println!(
+                        "{vis}mod \"{name}\" (#{}); {path}\n{:#?}",
+                        usize::from(type_id),
+                        module
+                    ),
+                    (_, None) => println!(
+                        "type {name}(#{}); {path}\n{:#?}",
+                        usize::from(type_id),
+                        prj.pool[type_id]
+                    ),
+                };
+            }
+        }
+        Ok(Response::Accept)
+    })
+}
diff --git a/cl-structures/src/intern_pool.rs b/cl-structures/src/intern_pool.rs
index ccd1f4d..dbba9bf 100644
--- a/cl-structures/src/intern_pool.rs
+++ b/cl-structures/src/intern_pool.rs
@@ -89,6 +89,13 @@ impl<T, ID: InternKey> Pool<T, ID> {
         self.pool.get_mut(index.get())
     }
 
+    pub fn iter(&self) -> impl Iterator<Item = &T> {
+        self.pool.iter()
+    }
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut T> {
+        self.pool.iter_mut()
+    }
+
     pub fn insert(&mut self, value: T) -> ID {
         let id = self.pool.len();
         self.pool.push(value);
diff --git a/cl-typeck/src/lib.rs b/cl-typeck/src/lib.rs
index a7a6357..ad7a738 100644
--- a/cl-typeck/src/lib.rs
+++ b/cl-typeck/src/lib.rs
@@ -1,7 +1,7 @@
 //! # The Conlang Type Checker
 //!
 //! As a statically typed language, Conlang requires a robust type checker to enforce correctness.
-
+#![feature(debug_closure_helpers)]
 #![warn(clippy::all)]
 
 /*
@@ -19,50 +19,161 @@ pub mod key {
 
     // define the index types
     make_intern_key! {
-        /// Uniquely represents a TypeDef in the TypeDef [Pool]
-        TypeID,
-        /// Uniquely represents a ValueDef in the ValueDef [Pool]
-        ValueID,
-        /// Uniquely represents a Module in the Module [Pool]
-        ModuleID,
+        /// Uniquely represents a [Def][1] in the [Def][1] [Pool]
+        ///
+        /// [1]: crate::definition::Def
+        DefID,
     }
 }
 
-pub mod typedef {
-    //! A TypeDef represents an item in the Type Namespace (a component of a
-    //! [Project](crate::project::Project)).
+pub mod definition {
+    use crate::{key::DefID, module::Module, type_kind::TypeKind, value_kind::ValueKind};
+    use cl_ast::{format::FmtPretty, Item, Meta, Visibility};
+    use std::fmt::Write;
 
-    use crate::key::{TypeID, ValueID};
-    use cl_ast::{Item, Visibility};
-
-    /// A TypeDef represents an item in the Type Namespace (a component of a
-    /// [Project](crate::project::Project)).
-    #[derive(Clone, Debug, PartialEq, Eq)]
-    pub struct TypeDef {
+    #[derive(Clone, PartialEq, Eq)]
+    pub struct Def {
         pub name: String,
-        /// The expanded form of the definition, with all fields properly typed.
-        /// This is filled in once all types are been enumerated.
-        pub kind: Option<TypeKind>,
-        pub definition: Item,
-        pub associated_values: Vec<ValueID>,
-        // TODO: Generic type parameters
+        pub vis: Visibility,
+        pub meta: Vec<Meta>,
+        pub kind: DefKind,
+        pub source: Option<Item>,
+        pub module: Module,
+    }
+
+    impl Default for Def {
+        fn default() -> Self {
+            Self {
+                name: Default::default(),
+                vis: Default::default(),
+                meta: Default::default(),
+                kind: DefKind::Type(TypeKind::Module),
+                source: Default::default(),
+                module: Default::default(),
+            }
+        }
+    }
+
+    impl Def {
+        pub fn new_module(
+            name: String,
+            vis: Visibility,
+            meta: Vec<Meta>,
+            parent: Option<DefID>,
+        ) -> Self {
+            Self {
+                name,
+                vis,
+                meta,
+                kind: DefKind::Type(TypeKind::Module),
+                source: None,
+                module: Module { parent, ..Default::default() },
+            }
+        }
+    }
+
+    impl std::fmt::Debug for Def {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { name, vis, meta, kind, source, module } = self;
+            f.debug_struct("Def")
+                .field("name", &name)
+                .field("vis", &vis)
+                .field_with("meta", |f| write!(f, "{meta:?}"))
+                .field("kind", &kind)
+                .field_with("source", |f| match source {
+                    Some(item) => write!(f.pretty(), "{{\n{item}\n}}"),
+                    None => todo!(),
+                })
+                .field("module", &module)
+                .finish()
+        }
     }
 
+    #[derive(Clone, Debug, PartialEq, Eq)]
+    pub enum DefKind {
+        /// A type, such as a ``
+        Type(TypeKind),
+        /// A value, such as a `const`, `static`, or `fn`
+        Value(ValueKind),
+    }
+
+    impl DefKind {
+        pub fn is_type(&self) -> bool {
+            matches!(self, Self::Type(_))
+        }
+        pub fn ty(&self) -> Option<&TypeKind> {
+            match self {
+                DefKind::Type(t) => Some(t),
+                _ => None,
+            }
+        }
+        pub fn is_value(&self) -> bool {
+            matches!(self, Self::Value(_))
+        }
+        pub fn value(&self) -> Option<&ValueKind> {
+            match self {
+                DefKind::Value(v) => Some(v),
+                _ => None,
+            }
+        }
+    }
+}
+
+pub mod type_kind {
+    //! A [TypeKind] represents an item in the Type Namespace
+    //! (a component of a [Project](crate::project::Project)).
+
+    use cl_ast::Visibility;
+    use std::{fmt::Debug, str::FromStr};
+
+    use crate::key::DefID;
+
+    /// The kind of a type
     #[derive(Clone, Debug, PartialEq, Eq)]
     pub enum TypeKind {
+        /// A type which has not yet been resolved
+        Undecided,
+        /// An alias for an already-defined type
+        Alias(Option<DefID>),
         /// A primitive type, built-in to the compiler
         Intrinsic(Intrinsic),
-        /// A user-defined structural product type
-        Struct(Vec<(String, Visibility, TypeID)>),
-        /// A user-defined union-like enum type
-        Enum(Vec<(String, TypeID)>),
-        /// An alias for an already-defined type
-        Alias(TypeID),
+        /// A user-defined abstract data type
+        Adt(Adt),
+        /// A reference to an already-defined type: &T
+        Ref(DefID),
+        /// A contiguous view of dynamically sized memory
+        Slice(DefID),
+        /// A function pointer which accepts multiple inputs and produces an output
+        FnPtr { args: Vec<DefID>, rety: DefID },
         /// The unit type
         Empty,
+        /// The never type
+        Never,
         /// The Self type
         SelfTy,
-        // TODO: union types, tuples, tuple structs maybe?
+        /// An untyped module
+        Module,
+    }
+
+    /// A user-defined Abstract Data Type
+    #[derive(Clone, Debug, PartialEq, Eq)]
+    pub enum Adt {
+        /// A union-like enum type
+        Enum(Vec<(String, DefID)>),
+        CLikeEnum(Vec<(String, u128)>),
+        /// An enum with no fields, which can never be constructed
+        FieldlessEnum,
+
+        /// A structural product type with named members
+        Struct(Vec<(String, Visibility, DefID)>),
+        /// A structural product type with unnamed members
+        TupleStruct(Vec<(Visibility, DefID)>),
+        /// A structural product type of neither named nor unnamed members
+        UnitStruct,
+
+        /// A choose your own undefined behavior type
+        /// TODO: should unions be a language feature?
+        Union(Vec<(String, DefID)>),
     }
 
     /// The set of compiler-intrinsic types.
@@ -70,37 +181,70 @@ pub mod typedef {
     #[allow(non_camel_case_types)]
     #[derive(Clone, Debug, PartialEq, Eq)]
     pub enum Intrinsic {
-        /// A 32-bit two's complement integer
-        i32,
-        /// A 32-bit unsigned integer
-        u32,
-        /// A boolean (`true` or `false`)
-        bool,
+        /// An 8-bit signed integer: `#[intrinsic = "i8"]`
+        I8,
+        /// A 16-bit signed integer: `#[intrinsic = "i16"]`
+        I16,
+        /// A 32-bit signed integer: `#[intrinsic = "i32"]`
+        I32,
+        /// A 64-bit signed integer: `#[intrinsic = "i32"]`
+        I64,
+        // /// A 128-bit signed integer: `#[intrinsic = "i32"]`
+        // I128,
+        /// An 8-bit unsigned integer: `#[intrinsic = "u8"]`
+        U8,
+        /// A 16-bit unsigned integer: `#[intrinsic = "u16"]`
+        U16,
+        /// A 32-bit unsigned integer: `#[intrinsic = "u32"]`
+        U32,
+        /// A 64-bit unsigned integer: `#[intrinsic = "u64"]`
+        U64,
+        // /// A 128-bit unsigned integer: `#[intrinsic = "u128"]`
+        // U128,
+        /// A boolean (`true` or `false`): `#[intrinsic = "bool"]`
+        Bool,
+    }
+
+    impl FromStr for Intrinsic {
+        type Err = ();
+
+        fn from_str(s: &str) -> Result<Self, Self::Err> {
+            Ok(match s {
+                "i8" => Intrinsic::I8,
+                "i16" => Intrinsic::I16,
+                "i32" => Intrinsic::I32,
+                "i64" => Intrinsic::I64,
+                "u8" => Intrinsic::U8,
+                "u16" => Intrinsic::U16,
+                "u32" => Intrinsic::U32,
+                "u64" => Intrinsic::U64,
+                "bool" => Intrinsic::Bool,
+                _ => Err(())?,
+            })
+        }
+    }
+
+    #[derive(Clone, Debug, PartialEq, Eq)]
+    pub enum Float {
+        F32 = 0x20,
+        F64,
     }
 }
 
-pub mod valdef {
-    //! A [ValueDef] represents an item in the Value Namespace (a component of a
-    //! [Project](crate::project::Project)).
+pub mod value_kind {
+    //! A [ValueKind] represents an item in the Value Namespace
+    //! (a component of a [Project](crate::project::Project)).
 
     use crate::typeref::TypeRef;
-    use cl_ast::{Block, Item};
-
-    /// A [ValueDef] represents an item in the Value Namespace (a component of a
-    /// [Project](crate::project::Project)).
-    #[derive(Clone, Debug, PartialEq, Eq)]
-    pub struct ValueDef {
-        pub name: String,
-        /// The expanded form of the definition, with all fields properly typed
-        pub kind: Option<ValueKind>,
-        pub definition: Item,
-    }
+    use cl_ast::Block;
 
     #[derive(Clone, Debug, PartialEq, Eq)]
     pub enum ValueKind {
+        Undecided,
         Const(TypeRef),
         Static(TypeRef),
         Fn {
+            // TODO: Store the variable bindings here!
             args: Vec<TypeRef>,
             rety: TypeRef,
             body: Block,
@@ -111,57 +255,532 @@ pub mod valdef {
 pub mod module {
     //! A [Module] is a node in the Module Tree (a component of a
     //! [Project](crate::project::Project))
-    use crate::key::{ModuleID, TypeID, ValueID};
+    use crate::key::DefID;
     use std::collections::HashMap;
 
     /// A [Module] is a node in the Module Tree (a component of a
     /// [Project](crate::project::Project)).
     #[derive(Clone, Debug, Default, PartialEq, Eq)]
     pub struct Module {
-        pub parent: Option<ModuleID>,
-        pub types: HashMap<String, TypeID>,
-        pub values: HashMap<String, ValueID>,
-        pub submodules: HashMap<String, ModuleID>,
+        pub parent: Option<DefID>,
+        pub types: HashMap<String, DefID>,
+        pub values: HashMap<String, DefID>,
+    }
+
+    impl Module {
+        pub fn new(parent: DefID) -> Self {
+            Self { parent: Some(parent), ..Default::default() }
+        }
+    }
+}
+
+pub mod path {
+    use cl_ast::{Path as AstPath, PathPart};
+
+    #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+    pub struct Path<'p> {
+        pub absolute: bool,
+        pub parts: &'p [PathPart],
+    }
+
+    impl<'p> Path<'p> {
+        pub fn new(path: &'p AstPath) -> Self {
+            let AstPath { absolute, parts } = path;
+            Self { absolute: *absolute, parts }
+        }
+        pub fn relative(self) -> Self {
+            Self { absolute: false, ..self }
+        }
+        pub fn pop_front(self) -> Option<Self> {
+            let Self { absolute, parts } = self;
+            Some(Self { absolute, parts: parts.get(1..)? })
+        }
+        pub fn is_empty(&self) -> bool {
+            self.parts.is_empty()
+        }
+        pub fn len(&self) -> usize {
+            self.parts.len()
+        }
+        pub fn front(&self) -> Option<&PathPart> {
+            self.parts.first()
+        }
+    }
+
+    impl<'p> From<&'p AstPath> for Path<'p> {
+        fn from(value: &'p AstPath) -> Self {
+            Self::new(value)
+        }
+    }
+    impl std::fmt::Display for Path<'_> {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            const SEPARATOR: &str = "::";
+            let Self { absolute, parts } = self;
+            if *absolute {
+                write!(f, "{SEPARATOR}")?
+            }
+            for (idx, part) in parts.iter().enumerate() {
+                write!(f, "{}{part}", if idx > 0 { SEPARATOR } else { "" })?;
+            }
+            Ok(())
+        }
     }
 }
 
 pub mod project {
+    use crate::{
+        definition::{Def, DefKind},
+        key::DefID,
+        path::Path,
+        type_kind::TypeKind,
+    };
+    use cl_ast::{Identifier, PathPart, Visibility};
     use cl_structures::intern_pool::Pool;
+    use std::ops::{Index, IndexMut};
+
+    #[derive(Clone, Debug, PartialEq, Eq)]
+    pub struct Project {
+        pub pool: Pool<Def, DefID>,
+        pub module_root: DefID,
+    }
+
+    impl Project {
+        pub fn new() -> Self {
+            Self::default()
+        }
+    }
+    impl Default for Project {
+        fn default() -> Self {
+            let mut pool = Pool::default();
+            let module_root = pool.insert(Def::default());
+            // Insert the Never(!) type
+            let never = pool.insert(Def {
+                name: String::from("!"),
+                vis: Visibility::Public,
+                kind: DefKind::Type(TypeKind::Never),
+                ..Default::default()
+            });
+            pool[module_root]
+                .module
+                .types
+                .insert(String::from("!"), never);
+            Self { pool, module_root }
+        }
+    }
+
+    impl Project {
+        pub fn parent_of(&self, module: DefID) -> Option<DefID> {
+            self[module].module.parent
+        }
+        pub fn root_of(&self, module: DefID) -> DefID {
+            match self.parent_of(module) {
+                Some(module) => self.root_of(module),
+                None => module,
+            }
+        }
+        /// Resolves a path within a module tree, finding the innermost module.
+        /// Returns the remaining path parts.
+        pub fn get_type<'a>(&self, path: Path<'a>, within: DefID) -> Option<(DefID, Path<'a>)> {
+            // TODO: Cache module lookups
+            if path.absolute {
+                self.get_type(path.relative(), self.root_of(within))
+            } else if let Some(front) = path.front() {
+                let module = &self[within].module;
+                match front {
+                    PathPart::SelfKw => self.get_type(path.pop_front()?, within),
+                    PathPart::SuperKw => self.get_type(path.pop_front()?, module.parent?),
+                    PathPart::Ident(Identifier(name)) => match module.types.get(name) {
+                        Some(&submodule) => self.get_type(path.pop_front()?, submodule),
+                        None => Some((within, path)),
+                    },
+                }
+            } else {
+                Some((within, path))
+            }
+        }
+
+        pub fn get_value<'a>(&self, path: Path<'a>, within: DefID) -> Option<(DefID, Path<'a>)> {
+            match path.front()? {
+                PathPart::Ident(Identifier(name)) => Some((
+                    self[within].module.values.get(name).copied()?,
+                    path.pop_front()?,
+                )),
+                _ => None,
+            }
+        }
+
+        #[rustfmt::skip]
+        pub fn insert_type(&mut self, name: String, value: Def, parent: DefID) -> Option<DefID> {
+            let id = self.pool.insert(value);
+            self[parent].module.types.insert(name, id)
+        }
+        #[rustfmt::skip]
+        pub fn insert_value(&mut self, name: String, value: Def, parent: DefID) -> Option<DefID> {
+            let id = self.pool.insert(value);
+            self[parent].module.values.insert(name, id)
+        }
+    }
+
+    /// Implements [Index] and [IndexMut] for [Project]: `self.table[ID] -> Definition`
+    macro_rules! impl_index {
+        ($(self.$table:ident[$idx:ty] -> $out:ty),*$(,)?) => {$(
+            impl Index<$idx> for Project {
+                type Output = $out;
+                fn index(&self, index: $idx) -> &Self::Output {
+                    &self.$table[index]
+                }
+            }
+            impl IndexMut<$idx> for Project {
+                fn index_mut(&mut self, index: $idx) -> &mut Self::Output {
+                    &mut self.$table[index]
+                }
+            }
+        )*};
+    }
+    impl_index! {
+        self.pool[DefID] -> Def,
+        // self.types[TypeID] -> TypeDef,
+        // self.values[ValueID] -> ValueDef,
+    }
+}
+
+pub mod name_collector {
+    //! Performs step 1 of type checking: Collecting all the names of things into [Module] units
 
     use crate::{
-        key::{ModuleID, TypeID, ValueID},
-        module::Module,
-        typedef::TypeDef,
-        valdef::ValueDef,
+        definition::{Def, DefKind},
+        key,
+        project::Project,
+        type_kind::{Adt, TypeKind},
+        value_kind::ValueKind,
     };
+    use cl_ast::*;
+    use std::ops::{Deref, DerefMut};
 
-    #[derive(Clone, Debug, Default, PartialEq, Eq)]
-    pub struct Project {
-        pub types: Pool<TypeDef, TypeID>,
-        pub values: Pool<ValueDef, ValueID>,
-        pub modules: Pool<Module, ModuleID>,
+    /// Collects types for future use
+    #[derive(Debug, PartialEq, Eq)]
+    pub struct NameCollector<'prj> {
+        /// A stack of the current modules
+        pub mod_stack: Vec<key::DefID>,
+        /// The [Project], the type checker and resolver's central data store
+        pub project: &'prj mut Project,
+    }
+
+    impl<'prj> NameCollector<'prj> {
+        pub fn new(project: &'prj mut Project) -> Self {
+            // create a root module
+            Self { mod_stack: vec![project.module_root], project }
+        }
+
+        /// Gets the currently traversed parent module
+        pub fn parent(&self) -> Option<key::DefID> {
+            self.mod_stack.last().copied()
+        }
+    }
+
+    impl Deref for NameCollector<'_> {
+        type Target = Project;
+        fn deref(&self) -> &Self::Target {
+            self.project
+        }
+    }
+    impl DerefMut for NameCollector<'_> {
+        fn deref_mut(&mut self) -> &mut Self::Target {
+            self.project
+        }
+    }
+
+    impl NameCollector<'_> {
+        pub fn file(&mut self, f: &File) -> Result<(), &'static str> {
+            let parent = self.parent().ok_or("No parent to add item to")?;
+
+            for item in &f.items {
+                let def = match &item.kind {
+                    // modules
+                    // types
+                    ItemKind::Module(_) => {
+                        self.module(item)?;
+                        continue;
+                    }
+                    ItemKind::Enum(_) => Some(self.ty_enum(item)?),
+                    ItemKind::Alias(_) => Some(self.ty_alias(item)?),
+                    ItemKind::Struct(_) => Some(self.ty_struct(item)?),
+                    // values processed by the value collector
+                    ItemKind::Const(_) => Some(self.val_const(item)?),
+                    ItemKind::Static(_) => Some(self.val_static(item)?),
+                    ItemKind::Function(_) => Some(self.val_function(item)?),
+                    ItemKind::Impl(_) => None,
+                };
+                let Some(def) = def else { continue };
+                match def.kind {
+                    DefKind::Type(_) => {
+                        if let Some(v) = self.insert_type(def.name.clone(), def, parent) {
+                            panic!("Redefinition of type {} ({v:?})!", self[v].name)
+                        }
+                    }
+                    DefKind::Value(_) => {
+                        if let Some(v) = self.insert_value(def.name.clone(), def, parent) {
+                            panic!("Redefinition of value {} ({v:?})!", self[v].name)
+                        }
+                    }
+                }
+            }
+            Ok(())
+        }
+
+        /// Collects a [Module]
+        pub fn module(&mut self, m: &Item) -> Result<(), &'static str> {
+            let Item { kind: ItemKind::Module(Module { name, kind }), vis, attrs, .. } = m else {
+                Err("module called on Item which was not an ItemKind::Module")?
+            };
+            let ModuleKind::Inline(kind) = kind else {
+                Err("Out-of-line modules not yet supported")?
+            };
+            let parent = self.parent().ok_or("No parent to add module to")?;
+
+            let module = self.pool.insert(Def::new_module(
+                name.0.clone(),
+                *vis,
+                attrs.meta.clone(),
+                Some(parent),
+            ));
+
+            self[parent]
+                .module
+                .types
+                .insert(name.0.clone(), module)
+                .is_some()
+                .then(|| panic!("Error: redefinition of module {name}"));
+
+            self.mod_stack.push(module);
+            let out = self.file(kind);
+            self.mod_stack.pop();
+
+            out
+        }
+    }
+    /// Type collection
+    impl NameCollector<'_> {
+        /// Collects an [Item] of type [ItemKind::Enum]
+        pub fn ty_enum(&mut self, item: &Item) -> Result<Def, &'static str> {
+            let Item { kind: ItemKind::Enum(Enum { name, kind }), vis, attrs, .. } = item else {
+                Err("Enum called on item which was not ItemKind::Enum")?
+            };
+            let kind = match kind {
+                EnumKind::NoVariants => DefKind::Type(TypeKind::Adt(Adt::FieldlessEnum)),
+                EnumKind::Variants(_) => DefKind::Type(TypeKind::Undecided),
+            };
+
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind,
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+
+        /// Collects an [Item] of type [ItemKind::Alias]
+        pub fn ty_alias(&mut self, item: &Item) -> Result<Def, &'static str> {
+            let Item { kind: ItemKind::Alias(Alias { to: name, from }), vis, attrs, .. } = item
+            else {
+                Err("Alias called on Item which was not ItemKind::Alias")?
+            };
+
+            let mut kind = match from {
+                Some(_) => DefKind::Type(TypeKind::Undecided),
+                None => DefKind::Type(TypeKind::Alias(None)),
+            };
+
+            for meta in &attrs.meta {
+                let Meta { name: meta_name, kind: meta_kind } = meta;
+                match (meta_name.0.as_str(), meta_kind) {
+                    ("intrinsic", MetaKind::Equals(Literal::String(intrinsic))) => {
+                        kind = DefKind::Type(TypeKind::Intrinsic(
+                            intrinsic.parse().map_err(|_| "unknown intrinsic type")?,
+                        ));
+                    }
+                    ("intrinsic", MetaKind::Plain) => {
+                        kind = DefKind::Type(TypeKind::Intrinsic(
+                            name.0.parse().map_err(|_| "Unknown intrinsic type")?,
+                        ))
+                    }
+                    _ => {}
+                }
+            }
+
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind,
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+
+        /// Collects an [Item] of type [ItemKind::Struct]
+        pub fn ty_struct(&mut self, item: &Item) -> Result<Def, &'static str> {
+            let Item { kind: ItemKind::Struct(Struct { name, kind }), vis, attrs, .. } = item
+            else {
+                Err("Struct called on item which was not ItemKind::Struct")?
+            };
+            let kind = match kind {
+                StructKind::Empty => DefKind::Type(TypeKind::Adt(Adt::UnitStruct)),
+                StructKind::Tuple(_) => DefKind::Type(TypeKind::Undecided),
+                StructKind::Struct(_) => DefKind::Type(TypeKind::Undecided),
+            };
+
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind,
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+    }
+    /// Value collection
+    impl NameCollector<'_> {
+        pub fn val_const(&mut self, item: &Item) -> Result<Def, &'static str> {
+            let Item { kind: ItemKind::Const(Const { name, .. }), vis, attrs, .. } = item else {
+                Err("Const called on Item which was not ItemKind::Const")?
+            };
+
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind: DefKind::Value(ValueKind::Undecided),
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+
+        pub fn val_static(&mut self, item: &Item) -> Result<Def, &'static str> {
+            let Item { kind: ItemKind::Static(Static { name, .. }), vis, attrs, .. } = item else {
+                Err("Static called on Item which was not ItemKind::Static")?
+            };
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind: DefKind::Type(TypeKind::Undecided),
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+
+        pub fn val_function(&mut self, item: &Item) -> Result<Def, &'static str> {
+            // TODO: treat function bodies like modules with internal items
+            let Item { kind: ItemKind::Function(Function { name, .. }), vis, attrs, .. } = item
+            else {
+                Err("val_function called on Item which was not ItemKind::Function")?
+            };
+            Ok(Def {
+                name: name.0.clone(),
+                vis: *vis,
+                meta: attrs.meta.clone(),
+                kind: DefKind::Value(ValueKind::Undecided),
+                source: Some(item.clone()),
+                module: Default::default(),
+            })
+        }
+    }
+}
+
+pub mod type_resolver {
+    //! Performs step 2 of type checking: Evaluating type definitions
+    #![allow(unused)]
+    use std::ops::{Deref, DerefMut};
+
+    use cl_ast::*;
+
+    use crate::{definition::Def, key::DefID, project::Project};
+
+    pub struct TypeResolver<'prj> {
+        pub project: &'prj mut Project,
+    }
+
+    impl Deref for TypeResolver<'_> {
+        type Target = Project;
+        fn deref(&self) -> &Self::Target {
+            self.project
+        }
+    }
+    impl DerefMut for TypeResolver<'_> {
+        fn deref_mut(&mut self) -> &mut Self::Target {
+            self.project
+        }
+    }
+
+    impl TypeResolver<'_> {
+        pub fn resolve(&mut self) -> Result<bool, &str> {
+            #![allow(unused)]
+            for typedef in self.pool.iter_mut().filter(|v| v.kind.is_type()) {
+                let Def { name, vis, meta: attr, kind, source: Some(ref definition), module: _ } =
+                    typedef
+                else {
+                    continue;
+                };
+                match &definition.kind {
+                    ItemKind::Alias(Alias { to: _, from: Some(from) }) => match &from.kind {
+                        TyKind::Never => todo!(),
+                        TyKind::Empty => todo!(),
+                        TyKind::SelfTy => todo!(),
+                        TyKind::Path(_) => todo!(),
+                        TyKind::Tuple(_) => todo!(),
+                        TyKind::Ref(_) => todo!(),
+                        TyKind::Fn(_) => todo!(),
+                    },
+                    ItemKind::Alias(_) => {}
+                    ItemKind::Const(_) => todo!(),
+                    ItemKind::Static(_) => todo!(),
+                    ItemKind::Module(_) => todo!(),
+                    ItemKind::Function(_) => {}
+                    ItemKind::Struct(_) => {}
+                    ItemKind::Enum(_) => {}
+                    ItemKind::Impl(_) => {}
+                }
+            }
+            Ok(true)
+        }
+
+        pub fn get_type(&self, kind: &TyKind) -> Option<DefID> {
+            match kind {
+                TyKind::Never => todo!(),
+                TyKind::Empty => todo!(),
+                TyKind::SelfTy => todo!(),
+                TyKind::Path(_) => todo!(),
+                TyKind::Tuple(_) => todo!(),
+                TyKind::Ref(_) => todo!(),
+                TyKind::Fn(_) => todo!(),
+            }
+            None
+        }
     }
 }
 
 pub mod typeref {
-    //! Stores type and referencce info
+    //! Stores type and reference info
 
-    use crate::key::TypeID;
+    use crate::key::DefID;
 
     /// The Type struct represents all valid types, and can be trivially equality-compared
     #[derive(Clone, Debug, PartialEq, Eq)]
     pub struct TypeRef {
         /// You can only have a pointer chain 65535 pointers long.
         ref_depth: u16,
-        /// Types can be [Generic](TKind::Generic) or [Concrete](TKind::Concrete)
+        /// Types can be [Generic](RefKind::Generic) or [Concrete](RefKind::Concrete)
         kind: RefKind,
     }
 
-    /// Types can be [Generic](TKind::Generic) or [Concrete](TKind::Concrete)
+    /// Types can be [Generic](RefKind::Generic) or [Concrete](RefKind::Concrete)
     #[derive(Clone, Debug, PartialEq, Eq)]
     pub enum RefKind {
-        /// A Concrete type has an associated [TypeDef](super::typedef::TypeDef)
-        Concrete(TypeID),
+        /// A Concrete type has an associated [Def](super::definition::Def)
+        Concrete(DefID),
         /// A Generic type is a *locally unique* comparable value,
         /// valid only until the end of its typing context.
         /// This is usually the surrounding function.
@@ -233,7 +852,58 @@ let rules: Hashmap<Operation, Vec<Rule>> {
 
 */
 
-/*
-    Potential solution:
-    Store reference to type field of each type expression in the AST
-*/
+pub mod rule {
+    use crate::{key::DefID, typeref::TypeRef};
+
+    pub struct Rule {
+        /// What is this Rule for?
+        pub operation: (),
+        /// What inputs does it take?
+        pub inputs: Vec<TypeRef>,
+        /// What output does it produce?
+        pub output: TypeRef,
+        /// Where did this rule come from?
+        pub through: Origin,
+    }
+
+    // TODO: Genericize
+    pub enum Operation {
+        Mul,
+        Div,
+        Rem,
+        Add,
+        Sub,
+
+        Deref,
+        Neg,
+        Not,
+        At,
+        Tilde,
+
+        Index,
+
+        If,
+        While,
+        For,
+    }
+
+    pub enum Origin {
+        /// This rule is built into the compiler
+        Intrinsic,
+        /// This rule is derived from an implementation on a type
+        Extrinsic(DefID),
+    }
+}
+
+pub mod typeck {
+    #![allow(unused)]
+    use cl_ast::*;
+
+    pub struct Context {
+        rules: (),
+    }
+
+    trait TypeCheck {}
+}
+
+//