snapshot

editor/src/ast.rs

@@ -1,13 +1,12 @@
 use crate::pattern::{Pattern2, PatternId};
 use crate::pool::{NodeId, PoolStr, PoolVec};
+use crate::types::{Type2, TypeId};
 use arraystring::{typenum::U30, ArrayString};
-use roc_can::def::Annotation;
 use roc_can::expr::Recursive;
 use roc_module::low_level::LowLevel;
 use roc_module::operator::CalledVia;
 use roc_module::symbol::Symbol;
 use roc_types::subs::Variable;
-use roc_types::types::Type;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum Problem {
@@ -197,39 +196,34 @@ pub enum Expr2 {
     RuntimeError(/* TODO make a version of RuntimeError that fits in 15B */),
 }
 
-#[derive(Debug)]
-pub struct Def {
-    pub pattern: NodeId<Pattern2>, // 3B
-    pub expr: NodeId<Expr2>,       // 3B
-    // TODO maybe need to combine these vars behind a pointer?
-    pub expr_var: Variable,                        // 4B
-    pub pattern_vars: PoolVec<(Symbol, Variable)>, // 4B
-    // TODO how big is an annotation? What about an Option<Annotation>?
-    pub annotation: Option<Annotation>, // ???
-}
-
 #[derive(Debug)]
 pub struct ValueDef {
-    pub pattern: PatternId,
-    pub expr_type: Option<Type>,
-    pub expr_var: Variable,
+    pattern: PatternId,                 // 4B
+    expr_type: Option<(Type2, Rigids)>, // ?
+    expr_var: Variable,                 // 4B
 }
 
 #[derive(Debug)]
 pub enum FunctionDef {
     WithAnnotation {
         name: Symbol,                          // 8B
-        arguments: PoolVec<(Pattern2, Type, Variable)>, // 8B
-        return_type: Type,                              // ?
-        return_var: Variable,                           // 4B
+        arguments: PoolVec<(Pattern2, Type2)>, // 8B
+        rigids: NodeId<Rigids>,                // 4B
+        return_type: TypeId,                   // 4B
     },
     NoAnnotation {
-        name: Symbol,
-        arguments: PoolVec<(Pattern2, Variable)>,
-        return_var: Variable,
+        name: Symbol,                             // 8B
+        arguments: PoolVec<(Pattern2, Variable)>, // 8B
+        return_var: Variable,                     // 4B
     },
 }
 
+#[derive(Debug)]
+pub struct Rigids {
+    named: PoolVec<(PoolStr, Variable)>, // 8B
+    unnamed: PoolVec<Variable>,          // 8B
+}
+
 /// This is overflow data from a Closure variant, which needs to store
 /// more than 32B of total data
 #[derive(Debug)]
@@ -247,17 +241,8 @@ pub struct WhenBranch {
     pub guard: Option<NodeId<Expr2>>, // 4B
 }
 
-pub type PatternId = NodeId<Pattern2>;
 pub type ExprId = NodeId<Expr2>;
 
-// We have a maximum of 65K pages.
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub struct ExprPoolId(u16);
-
-/// Each of these is the index of one 16B node inside a page's 4096B
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub struct ExprPoolSlot(u8);
-
 #[test]
 fn size_of_expr() {
     assert_eq!(std::mem::size_of::<Expr2>(), crate::pool::NODE_BYTES);

editor/src/expr.rs

@@ -2,7 +2,11 @@
 #![allow(dead_code)]
 #![allow(unused_imports)]
 use crate::ast::{Expr2, ExprId, FloatVal, IntStyle, IntVal};
+use crate::pattern::to_pattern2;
 use crate::pool::{NodeId, Pool, PoolStr, PoolVec};
+use crate::types::{Type2, TypeId};
+use bumpalo::Bump;
+use inlinable_string::InlinableString;
 use roc_can::expr::Output;
 use roc_can::expr::Recursive;
 use roc_can::num::{finish_parsing_base, finish_parsing_float, finish_parsing_int};
@@ -18,33 +22,37 @@ use roc_region::all::{Located, Region};
 use roc_types::subs::{VarStore, Variable};
 
 pub struct Env<'a> {
-    home: ModuleId,
-    var_store: VarStore,
-    pool: &'a mut Pool,
+    pub home: ModuleId,
+    pub var_store: VarStore,
+    pub pool: &'a mut Pool,
+    pub arena: &'a Bump,
 
-    // module_ids: &'a ModuleIds,
-    ident_ids: IdentIds,
+    pub dep_idents: MutMap<ModuleId, IdentIds>,
+    pub module_ids: &'a ModuleIds,
+    pub ident_ids: IdentIds,
 
-    closures: MutMap<Symbol, References>,
+    pub closures: MutMap<Symbol, References>,
+    /// Symbols which were referenced by qualified lookups.
+    pub qualified_lookups: MutSet<Symbol>,
 
-    top_level_symbols: MutSet<Symbol>,
+    pub top_level_symbols: MutSet<Symbol>,
 
-    closure_name_symbol: Option<Symbol>,
+    pub closure_name_symbol: Option<Symbol>,
 }
 
 impl<'a> Env<'a> {
-    fn add<T>(&mut self, item: T, region: Region) -> NodeId<T> {
+    pub fn add<T>(&mut self, item: T, region: Region) -> NodeId<T> {
         let id = self.pool.add(item);
         self.set_region(id, region);
 
         id
     }
 
-    fn problem(&mut self, _problem: Problem) {
+    pub fn problem(&mut self, _problem: Problem) {
         todo!();
     }
 
-    fn set_region<T>(&mut self, _node_id: NodeId<T>, _region: Region) {
+    pub fn set_region<T>(&mut self, _node_id: NodeId<T>, _region: Region) {
         todo!();
     }
 
@@ -62,16 +70,80 @@ impl<'a> Env<'a> {
 
         Symbol::new(self.home, ident_id)
     }
-}
 
-pub fn to_pattern2<'a>(
-    _env: &mut Env<'a>,
-    _scope: &mut Scope,
-    _pattern_type: roc_parse::pattern::PatternType,
-    _pattern: &roc_parse::ast::Pattern<'a>,
-    _region: Region,
-) -> (Output, crate::ast::Pattern2) {
-    todo!()
+    /// Returns Err if the symbol resolved, but it was not exposed by the given module
+    pub fn qualified_lookup(
+        &mut self,
+        module_name: &str,
+        ident: &str,
+        region: Region,
+    ) -> Result<Symbol, RuntimeError> {
+        debug_assert!(
+            !module_name.is_empty(),
+            "Called env.qualified_lookup with an unqualified ident: {:?}",
+            ident
+        );
+
+        let module_name: InlinableString = module_name.into();
+
+        match self.module_ids.get_id(&module_name) {
+            Some(&module_id) => {
+                let ident: InlinableString = ident.into();
+
+                // You can do qualified lookups on your own module, e.g.
+                // if I'm in the Foo module, I can do a `Foo.bar` lookup.
+                if module_id == self.home {
+                    match self.ident_ids.get_id(&ident) {
+                        Some(ident_id) => {
+                            let symbol = Symbol::new(module_id, *ident_id);
+
+                            self.qualified_lookups.insert(symbol);
+
+                            Ok(symbol)
+                        }
+                        None => Err(RuntimeError::LookupNotInScope(
+                            Located {
+                                value: ident,
+                                region,
+                            },
+                            self.ident_ids
+                                .idents()
+                                .map(|(_, string)| string.as_ref().into())
+                                .collect(),
+                        )),
+                    }
+                } else {
+                    match self
+                        .dep_idents
+                        .get(&module_id)
+                        .and_then(|exposed_ids| exposed_ids.get_id(&ident))
+                    {
+                        Some(ident_id) => {
+                            let symbol = Symbol::new(module_id, *ident_id);
+
+                            self.qualified_lookups.insert(symbol);
+
+                            Ok(symbol)
+                        }
+                        None => Err(RuntimeError::ValueNotExposed {
+                            module_name,
+                            ident,
+                            region,
+                        }),
+                    }
+                }
+            }
+            None => Err(RuntimeError::ModuleNotImported {
+                module_name,
+                imported_modules: self
+                    .module_ids
+                    .available_modules()
+                    .map(|string| string.as_ref().into())
+                    .collect(),
+                region,
+            }),
+        }
+    }
 }
 
 const ZERO: Region = Region::zero();

editor/src/lib.rs

@@ -28,7 +28,9 @@ mod ortho;
 mod pattern;
 pub mod pool;
 mod rect;
+mod scope;
 pub mod text;
+mod types;
 mod util;
 mod vertex;
 

editor/src/pattern.rs

@@ -1,13 +1,13 @@
+use crate::ast::{ExprId, FloatVal, IntVal};
+use crate::expr::Env;
 use crate::pool::{NodeId, Pool, PoolStr, PoolVec};
-use arraystring::{typenum::U30, ArrayString};
-use roc_can::def::Annotation;
-use roc_can::expr::Recursive;
-use roc_module::low_level::LowLevel;
-use roc_module::operator::CalledVia;
+use roc_can::expr::Output;
+use roc_can::scope::Scope;
 use roc_module::symbol::Symbol;
-use roc_region::all::{Located, Region};
+use roc_region::all::Region;
 use roc_types::subs::Variable;
-use roc_types::types::Type;
+
+pub type PatternId = NodeId<Pattern2>;
 
 #[derive(Debug)]
 pub enum Pattern2 {
@@ -66,6 +66,16 @@ pub enum MalformedPatternProblem {
     QualifiedIdentifier,
 }
 
+pub fn to_pattern2<'a>(
+    _env: &mut Env<'a>,
+    _scope: &mut Scope,
+    _pattern_type: roc_parse::pattern::PatternType,
+    _pattern: &roc_parse::ast::Pattern<'a>,
+    _region: Region,
+) -> (Output, Pattern2) {
+    todo!()
+}
+
 pub fn symbols_from_pattern(pool: &Pool, initial: &Pattern2) -> Vec<Symbol> {
     use Pattern2::*;
     let mut symbols = Vec::new();

editor/src/pool.rs

@@ -244,6 +244,15 @@ impl PoolStr {
             }
         }
     }
+
+    pub fn duplicate(&self) -> Self {
+        // Question: should this fully clone, or is a shallow copy
+        // (and the aliasing it entails) OK?
+        Self {
+            first_node_id: self.first_node_id,
+            len: self.len,
+        }
+    }
 }
 
 /// An array of at most 2^32 pool-allocated nodes.
@@ -275,6 +284,14 @@ impl<'a, T: 'a + Sized> PoolVec<T> {
         }
     }
 
+    pub fn len(&self) -> usize {
+        self.len as usize
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
     pub fn new<I: ExactSizeIterator<Item = T>>(nodes: I, pool: &mut Pool) -> Self {
         debug_assert!(nodes.len() <= u32::MAX as usize);
         debug_assert!(size_of::<T>() <= NODE_BYTES);
@@ -348,6 +365,15 @@ impl<'a, T: 'a + Sized> PoolVec<T> {
         }
     }
 
+    pub fn duplicate(&self) -> Self {
+        // Question: should this fully clone, or is a shallow copy
+        // (and the aliasing it entails) OK?
+        Self {
+            first_node_id: self.first_node_id,
+            len: self.len,
+        }
+    }
+
     pub fn free<S>(self, pool: &'a mut Pool) {
         // zero out the memory
         unsafe {
@@ -525,3 +551,37 @@ impl<T> Iterator for PoolVecIterNodeIds<T> {
         }
     }
 }
+
+/// TODO
+#[derive(Debug)]
+pub struct PoolMap<K, V> {
+    first_node_id: NodeId<(K, V)>,
+    len: u32,
+}
+
+#[test]
+fn pool_map_size() {
+    assert_eq!(size_of::<PoolMap<(), ()>>(), 8);
+}
+
+impl<K: Eq, V> PoolMap<K, V> {
+    pub fn empty(pool: &mut Pool) -> Self {
+        todo!()
+    }
+
+    pub fn with_capacity(pool: &mut Pool, size: u32) -> Self {
+        todo!()
+    }
+
+    pub fn insert(&mut self, pool: &mut Pool, k: K, v: V) -> Option<(K, V)> {
+        todo!()
+    }
+
+    pub fn remove(&mut self, pool: &mut Pool, k: &K) -> Option<(K, V)> {
+        todo!()
+    }
+
+    pub fn contains(&mut self, pool: &mut Pool, k: &K) -> bool {
+        todo!()
+    }
+}

editor/src/scope.rs

@@ -0,0 +1,221 @@
+use crate::pool::{Pool, PoolStr, PoolVec};
+use crate::types::{Alias, TypeId};
+use roc_collections::all::{MutMap, MutSet};
+use roc_module::ident::{Ident, Lowercase};
+use roc_module::symbol::{IdentIds, ModuleId, Symbol};
+use roc_problem::can::RuntimeError;
+use roc_region::all::{Located, Region};
+use roc_types::subs::{VarStore, Variable};
+
+fn solved_type_to_type_id() -> TypeId {
+    todo!()
+}
+
+#[derive(Debug)]
+pub struct Scope {
+    /// All the identifiers in scope, mapped to were they were defined and
+    /// the Symbol they resolve to.
+    idents: MutMap<Ident, (Symbol, Region)>,
+
+    /// A cache of all the symbols in scope. This makes lookups much
+    /// faster when checking for unused defs and unused arguments.
+    symbols: MutMap<Symbol, Region>,
+
+    /// The type aliases currently in scope
+    /// Uses BTreeMap because HashMap requires elements are Clone
+    aliases: MutMap<Symbol, Alias>,
+
+    /// The current module being processed. This will be used to turn
+    /// unqualified idents into Symbols.
+    home: ModuleId,
+}
+
+impl Scope {
+    pub fn new(home: ModuleId, pool: &mut Pool, var_store: &mut VarStore) -> Scope {
+        use roc_types::solved_types::{BuiltinAlias, FreeVars};
+        let solved_aliases = roc_types::builtin_aliases::aliases();
+        let mut aliases = MutMap::default();
+
+        for (symbol, builtin_alias) in solved_aliases {
+            let BuiltinAlias { region, vars, typ } = builtin_alias;
+
+            let mut free_vars = FreeVars::default();
+            let typ = solved_type_to_type_id();
+            // roc_types::solved_types::to_type(&typ, &mut free_vars, var_store);
+
+            // make sure to sort these variables to make them line up with the type arguments
+            let mut type_variables: Vec<_> = free_vars.unnamed_vars.into_iter().collect();
+            type_variables.sort();
+
+            debug_assert_eq!(vars.len(), type_variables.len());
+            let mut variables = PoolVec::with_capacity(vars.len() as u32, pool);
+
+            let it = variables
+                .iter_node_ids()
+                .zip(vars.iter())
+                .zip(type_variables);
+            for ((node_id, loc_name), (_, var)) in it {
+                // TODO region is ignored, but "fake" anyway. How to resolve?
+                let name = PoolStr::new(loc_name.value.as_str(), pool);
+                pool[node_id] = (name, var);
+            }
+
+            let alias = Alias {
+                actual: typ,
+                /// We know that builtin aliases have no hiddden variables (e.g. in closures)
+                hidden_variables: PoolVec::empty(pool),
+                targs: variables,
+            };
+
+            aliases.insert(symbol, alias);
+        }
+
+        let idents = Symbol::default_in_scope();
+        let idents: MutMap<_, _> = idents.into_iter().collect();
+
+        Scope {
+            home,
+            idents,
+            symbols: MutMap::default(),
+            aliases,
+        }
+    }
+
+    pub fn idents(&self) -> impl Iterator<Item = (&Ident, &(Symbol, Region))> {
+        self.idents.iter()
+    }
+
+    pub fn symbols(&self) -> impl Iterator<Item = (Symbol, Region)> + '_ {
+        self.symbols.iter().map(|(x, y)| (*x, *y))
+    }
+
+    pub fn contains_ident(&self, ident: &Ident) -> bool {
+        self.idents.contains_key(ident)
+    }
+
+    pub fn contains_symbol(&self, symbol: Symbol) -> bool {
+        self.symbols.contains_key(&symbol)
+    }
+
+    pub fn num_idents(&self) -> usize {
+        self.idents.len()
+    }
+
+    pub fn lookup(&mut self, ident: &Ident, region: Region) -> Result<Symbol, RuntimeError> {
+        match self.idents.get(ident) {
+            Some((symbol, _)) => Ok(*symbol),
+            None => Err(RuntimeError::LookupNotInScope(
+                Located {
+                    region,
+                    value: ident.clone().into(),
+                },
+                self.idents.keys().map(|v| v.as_ref().into()).collect(),
+            )),
+        }
+    }
+
+    pub fn lookup_alias(&self, symbol: Symbol) -> Option<&Alias> {
+        self.aliases.get(&symbol)
+    }
+
+    /// Introduce a new ident to scope.
+    ///
+    /// Returns Err if this would shadow an existing ident, including the
+    /// Symbol and Region of the ident we already had in scope under that name.
+    pub fn introduce(
+        &mut self,
+        ident: Ident,
+        exposed_ident_ids: &IdentIds,
+        all_ident_ids: &mut IdentIds,
+        region: Region,
+    ) -> Result<Symbol, (Region, Located<Ident>)> {
+        match self.idents.get(&ident) {
+            Some((_, original_region)) => {
+                let shadow = Located {
+                    value: ident,
+                    region,
+                };
+
+                Err((*original_region, shadow))
+            }
+            None => {
+                // If this IdentId was already added previously
+                // when the value was exposed in the module header,
+                // use that existing IdentId. Otherwise, create a fresh one.
+                let ident_id = match exposed_ident_ids.get_id(&ident.as_inline_str()) {
+                    Some(ident_id) => *ident_id,
+                    None => all_ident_ids.add(ident.clone().into()),
+                };
+
+                let symbol = Symbol::new(self.home, ident_id);
+
+                self.symbols.insert(symbol, region);
+                self.idents.insert(ident, (symbol, region));
+
+                Ok(symbol)
+            }
+        }
+    }
+
+    /// Ignore an identifier.
+    ///
+    /// Used for record guards like { x: Just _ }
+    pub fn ignore(&mut self, ident: Ident, all_ident_ids: &mut IdentIds) -> Symbol {
+        let ident_id = all_ident_ids.add(ident.into());
+        Symbol::new(self.home, ident_id)
+    }
+
+    /// Import a Symbol from another module into this module's top-level scope.
+    ///
+    /// Returns Err if this would shadow an existing ident, including the
+    /// Symbol and Region of the ident we already had in scope under that name.
+    pub fn import(
+        &mut self,
+        ident: Ident,
+        symbol: Symbol,
+        region: Region,
+    ) -> Result<(), (Symbol, Region)> {
+        match self.idents.get(&ident) {
+            Some(shadowed) => Err(*shadowed),
+            None => {
+                self.symbols.insert(symbol, region);
+                self.idents.insert(ident, (symbol, region));
+
+                Ok(())
+            }
+        }
+    }
+
+    pub fn add_alias(
+        &mut self,
+        pool: &mut Pool,
+        name: Symbol,
+        vars: PoolVec<(PoolStr, Variable)>,
+        typ: TypeId,
+    ) {
+        let mut hidden_variables = MutSet::default();
+        hidden_variables.extend(typ.variables(pool));
+
+        for loc_var in vars.iter(pool) {
+            hidden_variables.remove(&loc_var.1);
+        }
+
+        let hidden_variables_vec = PoolVec::with_capacity(hidden_variables.len() as u32, pool);
+
+        for (node_id, var) in hidden_variables_vec.iter_node_ids().zip(hidden_variables) {
+            pool[node_id] = var;
+        }
+
+        let alias = Alias {
+            targs: vars,
+            hidden_variables: hidden_variables_vec,
+            actual: typ,
+        };
+
+        self.aliases.insert(name, alias);
+    }
+
+    pub fn contains_alias(&mut self, name: Symbol) -> bool {
+        self.aliases.contains_key(&name)
+    }
+}

editor/src/types.rs

@@ -0,0 +1,314 @@
+use crate::expr::Env;
+use crate::pool::{NodeId, Pool, PoolStr, PoolVec};
+use crate::scope::Scope;
+// use roc_can::expr::Output;
+use roc_collections::all::{MutMap, MutSet};
+use roc_module::ident::Ident;
+use roc_module::symbol::Symbol;
+use roc_region::all::{Located, Region};
+use roc_types::subs::Variable;
+use roc_types::types::{Problem, RecordField};
+
+pub type TypeId = NodeId<Type2>;
+
+#[derive(Debug)]
+pub enum Type2 {
+    Variable(Variable),
+
+    Alias(Symbol, PoolVec<(PoolStr, TypeId)>, TypeId), // 20B = 8B + 8B + 4B
+    HostExposedAlias {
+        name: Symbol,                          // 8B
+        arguments: PoolVec<(PoolStr, TypeId)>, // 8B
+        actual_var: Variable,                  // 4B
+        actual: TypeId,                        // 4B
+    },
+
+    EmptyTagUnion,
+    TagUnion(PoolVec<(PoolStr, PoolVec<Type2>)>, TypeId),
+    RecursiveTagUnion(Variable, PoolVec<(PoolStr, PoolVec<Type2>)>, TypeId),
+
+    EmptyRec,
+    Record(PoolVec<(PoolStr, RecordField<Type2>)>, TypeId),
+
+    Function(PoolVec<Type2>, TypeId, TypeId), // 16B = 8B + 4B + 4B
+    Apply(Symbol, PoolVec<Type2>),            // 16B = 8B + 8B
+
+    Erroneous(roc_types::types::Problem),
+}
+
+impl Type2 {
+    fn substitute(_pool: &mut Pool, _subs: &MutMap<Variable, TypeId>, _type_id: TypeId) {
+        todo!()
+    }
+    pub fn variables(&self, _pool: &mut Pool) -> MutSet<Variable> {
+        todo!()
+    }
+}
+
+impl NodeId<Type2> {
+    pub fn variables(&self, _pool: &mut Pool) -> MutSet<Variable> {
+        todo!()
+    }
+}
+
+/// A temporary data structure to return a bunch of values to Def construction
+pub enum Annotation2<'a> {
+    FunctionWithAliases {
+        annotation: Type2,
+        arguments: PoolVec<Type2>,
+        closure_type_id: TypeId,
+        return_type_id: TypeId,
+        named_rigids: MutMap<&'a str, Variable>,
+        unnamed_rigids: MutSet<Variable>,
+    },
+    Function {
+        arguments: PoolVec<Type2>,
+        closure_type_id: TypeId,
+        return_type_id: TypeId,
+        named_rigids: MutMap<&'a str, Variable>,
+        unnamed_rigids: MutSet<Variable>,
+    },
+    Value {
+        annotation: Type2,
+        named_rigids: MutMap<&'a str, Variable>,
+        unnamed_rigids: MutSet<Variable>,
+    },
+    Erroneous(roc_types::types::Problem),
+}
+
+pub fn to_annotation2<'a>(
+    env: &mut Env,
+    scope: &mut Scope,
+    annotation: &'a roc_parse::ast::TypeAnnotation<'a>,
+    _region: Region,
+) -> Annotation2<'a> {
+    use roc_parse::ast::TypeAnnotation::*;
+
+    let mut rigids = Rigids::default();
+    let mut alias_stack = Vec::new();
+    // let mut as_alias_stack = Vec::new();
+
+    // we dealias until we hit a non-alias, then we either hit a function type (and produce a
+    // function annotation) or anything else (and produce a value annotation)
+    match annotation {
+        Function(argument_types, return_type) => {
+            //
+            let arguments = PoolVec::with_capacity(argument_types.len() as u32, env.pool);
+
+            for (type_id, loc_arg) in arguments.iter_node_ids().zip(argument_types.iter()) {
+                as_type_id(
+                    env,
+                    scope,
+                    &mut rigids,
+                    type_id,
+                    &loc_arg.value,
+                    loc_arg.region,
+                );
+            }
+
+            let return_type_id = to_type_id(
+                env,
+                scope,
+                &mut rigids,
+                &return_type.value,
+                return_type.region,
+            );
+
+            let closure_type = Type2::Variable(env.var_store.fresh());
+            let closure_type_id = env.pool.add(closure_type);
+
+            let Rigids { named, unnamed, .. } = rigids;
+
+            // if alias_stack.is_empty() && as_alias_stack.is_empty() {
+            if alias_stack.is_empty() {
+                Annotation2::Function {
+                    arguments,
+                    closure_type_id,
+                    return_type_id,
+                    named_rigids: named,
+                    unnamed_rigids: unnamed,
+                }
+            } else {
+                let mut annotation =
+                    Type2::Function(arguments.duplicate(), closure_type_id, return_type_id);
+                for (name, targs) in alias_stack.into_iter().rev().peekable() {
+                    let type_id = env.pool.add(annotation);
+
+                    annotation = Type2::Alias(name, targs, type_id);
+                }
+
+                Annotation2::FunctionWithAliases {
+                    annotation,
+                    arguments,
+                    closure_type_id,
+                    return_type_id,
+                    named_rigids: named,
+                    unnamed_rigids: unnamed,
+                }
+            }
+        }
+        Apply(module_name, ident, targs) => {
+            todo!()
+        }
+    }
+}
+
+#[derive(Default)]
+struct Rigids<'a> {
+    named: MutMap<&'a str, Variable>,
+    unnamed: MutSet<Variable>,
+    hidden: MutSet<Variable>,
+}
+
+pub fn to_type_id(
+    env: &mut Env,
+    scope: &mut Scope,
+    rigids: &mut Rigids,
+    annotation: &roc_parse::ast::TypeAnnotation,
+    region: Region,
+) -> TypeId {
+    let type2 = to_type2(env, scope, rigids, annotation);
+
+    env.add(type2, region)
+}
+
+pub fn as_type_id(
+    env: &mut Env,
+    scope: &mut Scope,
+    rigids: &mut Rigids,
+    type_id: TypeId,
+    annotation: &roc_parse::ast::TypeAnnotation,
+    region: Region,
+) {
+    let type2 = to_type2(env, scope, rigids, annotation);
+
+    env.pool[type_id] = type2;
+    env.set_region(type_id, region);
+}
+
+pub fn to_type2(
+    env: &mut Env,
+    scope: &mut Scope,
+    rigids: &mut Rigids,
+    annotation: &roc_parse::ast::TypeAnnotation,
+) -> Type2 {
+    todo!()
+}
+
+enum TypeApply {
+    Apply(Symbol, PoolVec<Type2>),
+    Alias(Symbol, PoolVec<(PoolStr, TypeId)>, TypeId),
+    Erroneous(roc_types::types::Problem),
+}
+
+fn to_type_apply(
+    env: &mut Env,
+    scope: &mut Scope,
+    rigids: &mut Rigids,
+    module_name: &str,
+    ident: &str,
+    type_arguments: &[Located<roc_parse::ast::TypeAnnotation>],
+    region: Region,
+) -> TypeApply {
+    let symbol = if module_name.is_empty() {
+        // Since module_name was empty, this is an unqualified type.
+        // Look it up in scope!
+        let ident: Ident = (*ident).into();
+
+        match scope.lookup(&ident, region) {
+            Ok(symbol) => symbol,
+            Err(problem) => {
+                env.problem(roc_problem::can::Problem::RuntimeError(problem));
+
+                return TypeApply::Erroneous(Problem::UnrecognizedIdent(ident.into()));
+            }
+        }
+    } else {
+        match env.qualified_lookup(module_name, ident, region) {
+            Ok(symbol) => symbol,
+            Err(problem) => {
+                // Either the module wasn't imported, or
+                // it was imported but it doesn't expose this ident.
+                env.problem(roc_problem::can::Problem::RuntimeError(problem));
+
+                return TypeApply::Erroneous(Problem::UnrecognizedIdent((*ident).into()));
+            }
+        }
+    };
+
+    let argument_type_ids = PoolVec::with_capacity(type_arguments.len() as u32, env.pool);
+
+    for (type_id, loc_arg) in argument_type_ids.iter_node_ids().zip(type_arguments.iter()) {
+        as_type_id(env, scope, rigids, type_id, &loc_arg.value, loc_arg.region);
+    }
+
+    let args = type_arguments;
+    let opt_alias = scope.lookup_alias(symbol);
+    match opt_alias {
+        Some(ref alias) => {
+            // use a known alias
+            let actual = alias.actual;
+            let mut substitutions: MutMap<Variable, TypeId> = MutMap::default();
+
+            if alias.targs.len() != args.len() {
+                let error = TypeApply::Erroneous(Problem::BadTypeArguments {
+                    symbol,
+                    region,
+                    alias_needs: alias.targs.len() as u8,
+                    type_got: args.len() as u8,
+                });
+                return error;
+            }
+
+            let arguments = PoolVec::with_capacity(type_arguments.len() as u32, env.pool);
+
+            let it = arguments.iter_node_ids().zip(
+                argument_type_ids
+                    .iter_node_ids()
+                    .zip(alias.targs.iter_node_ids()),
+            );
+
+            for (node_id, (type_id, loc_var_id)) in it {
+                let loc_var = &env.pool[loc_var_id];
+                let name = loc_var.0.duplicate();
+                let var = loc_var.1;
+
+                env.pool[node_id] = (name, type_id);
+
+                substitutions.insert(var, type_id);
+            }
+
+            // make sure the recursion variable is freshly instantiated
+            // have to allocate these outside of the if for lifetime reasons...
+            let new = env.var_store.fresh();
+            let fresh = env.pool.add(Type2::Variable(new));
+            if let Type2::RecursiveTagUnion(rvar, ref tags, ext) = &mut env.pool[actual] {
+                substitutions.insert(*rvar, fresh);
+
+                env.pool[actual] = Type2::RecursiveTagUnion(new, tags.duplicate(), *ext);
+            }
+
+            // make sure hidden variables are freshly instantiated
+            for var_id in alias.hidden_variables.iter_node_ids() {
+                let var = env.pool[var_id];
+                let fresh = env.pool.add(Type2::Variable(env.var_store.fresh()));
+                substitutions.insert(var, fresh);
+            }
+
+            // instantiate variables
+            Type2::substitute(env.pool, &substitutions, actual);
+
+            TypeApply::Alias(symbol, arguments, actual)
+        }
+        None => TypeApply::Apply(symbol, argument_type_ids),
+    }
+}
+
+#[derive(Debug)]
+pub struct Alias {
+    pub targs: PoolVec<(PoolStr, Variable)>,
+    pub actual: TypeId,
+
+    /// hidden type variables, like the closure variable in `a -> b`
+    pub hidden_variables: PoolVec<Variable>,
+}