idk man..

src/ast2/biunification.rs

@@ -5,30 +5,43 @@
 // Visitor pattern has lots of unused arguments
 #![allow(unused_variables)]
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
+
+use crate::ast2::tag::{AstNode, AstNodeExt};
 
 use super::{Ast, Index, intern, visitor::AstVisitorTrait};
 
 type Id = u32;
 
-enum Type {
-    Reified(intern::Index),
-    Variable(Id),
+trait TypeVariance {
+    type T;
+    type Opposite;
+}
+
+#[derive(Debug, Clone)]
+enum TypeHead<T: TypeVariance> {
+    Real(intern::Index),
+    Function { args: Vec<T::T>, ret: T::Opposite },
 }
 
 /// Variance of a type parameter or constraint.
 /// A function of type `A -> B` is covariant in `B` and contravariant in `A`.
-/// This means that a type `T` may be substituted for `A` if `T` is a subtype of `A`, but
-/// a type `T` may only be substituted for `B` if `T` is a supertype of `B`.
+/// This means that a type `T` may be substituted for `A` if `T` is a subtype of
+/// `A`, that is, every `T` is also an `A`,
+/// but a type `T` may only be substituted for `B` if `T` is a supertype of `B`,
+/// that is, every `B` is also a `T`.
 ///
 /// Namely, in a type system with `int` and `nat <: int`, for a function `f: int
 /// -> int` in the expression `let u: int = 3; let t: nat = f(u);`, `u` may
 /// safely be used as an argument to `f` because `nat <: int`, but `f(u`)` may
 /// not be assigned to `t` because `int <: nat` is not true.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
 enum Variance {
-    #[doc(alias = "Positive")]
+    /// A Positive, or union relationship between types.
+    /// used in value-places.
     Covariant,
-    #[doc(alias = "Negative")]
+    /// A Negative, or intersection relationship between types.
+    /// used in use-places.
     Contravariant,
 }
 
@@ -37,27 +50,81 @@ struct Value(Id);
 #[derive(Debug, Clone, Copy)]
 struct Use(Id);
 
+impl TypeVariance for Value {
+    type T = Value;
+    type Opposite = Use;
+}
+
+impl TypeVariance for Use {
+    type T = Use;
+    type Opposite = Value;
+}
+
 /// Typechecking error.
 #[derive(Debug, Clone, thiserror::Error)]
 enum Error {
     #[error("Unimplemented feature")]
     Unimplemented,
+    #[error("{0}")]
+    StringError(String),
 }
 
 type Result<T> = std::result::Result<T, Error>;
 
 struct Bindings {
-    inner: HashMap<super::Index, Value>,
+    next_id: Id,
+    inner: HashMap<super::Index, Id>,
+    bounds: HashSet<(Id, Id, Variance)>,
+    types: HashMap<Id, intern::Index>,
+}
+
+impl Bindings {
+    fn new() -> Self {
+        Bindings {
+            next_id: 1,
+            inner: HashMap::new(),
+            bounds: HashSet::new(),
+            types: HashMap::new(),
+        }
+    }
+
+    fn new_id(&mut self) -> Id {
+        let id = self.next_id;
+        self.next_id += 1;
+        id
+    }
+
+    fn get_or_create(&mut self, idx: super::Index) -> Id {
+        self.inner.get(&idx).copied().unwrap_or_else(|| {
+            let id = self.new_id();
+            self.inner.insert(idx, id);
+            id
+        })
+    }
+
+    /// retrieves the type Id for the given ast node.
+    fn get(&self, idx: super::Index) -> Option<Id> {
+        self.inner.get(&idx).copied()
+    }
+
+    /// inserts a proper type for `id`.
+    fn insert_type(&mut self, id: Id, ty: intern::Index) {
+        self.types.insert(id, ty);
+    }
 }
 
 struct TypeChecker<'a> {
     pool: &'a mut intern::InternPool,
+    bindings: Bindings,
 }
 
 // Core
 impl TypeChecker<'_> {
     pub fn new(pool: &mut intern::InternPool) -> TypeChecker {
-        TypeChecker { pool }
+        TypeChecker {
+            pool,
+            bindings: Bindings::new(),
+        }
     }
 
     fn var(&mut self) -> (Value, Use) {
@@ -73,6 +140,33 @@ impl<'a> AstVisitorTrait<&'a Ast> for TypeChecker<'_> {
 
     const UNIMPL: Self::Error = Error::Unimplemented;
 
+    fn visit_interned_type_impl(
+        &mut self,
+        ast: &'a Ast,
+        idx: Index,
+        intern: intern::Index,
+    ) -> std::result::Result<Self::Value, Self::Error> {
+        let id = self.bindings.get_or_create(idx);
+        match self.pool.get_key(intern) {
+            intern::Key::SimpleType {
+                ty: intern::SimpleType::ComptimeInt,
+            } => {
+                // This is a type variable.
+            }
+            intern::Key::SimpleType { .. }
+            | intern::Key::PointerType { .. }
+            | intern::Key::ArrayType { .. }
+            | intern::Key::FunctionType { .. }
+            | intern::Key::StructType { .. } => {
+                // This is a real type.
+                self.bindings.insert_type(id, intern);
+            }
+            _ => unreachable!(),
+        }
+
+        Ok(Value(id))
+    }
+
     fn visit_constant_impl(
         &mut self,
         ast: &'a Ast,
@@ -80,8 +174,30 @@ impl<'a> AstVisitorTrait<&'a Ast> for TypeChecker<'_> {
         ty: Index,
         value: intern::Index,
     ) -> std::result::Result<Self::Value, Self::Error> {
-        // constants may be of type `comptime_int`, which is a special type that
-        // cannot exist at runtime.
+        // get type from the pool
+
+        let AstNode::InternedType { intern } = ast.get_ast_node(ty) else {
+            panic!(
+                "Expected an interned type node, got {:?}",
+                ast.get_ast_node(ty)
+            );
+        };
+
+        match self.pool.get_key(intern) {
+            intern::Key::SimpleType {
+                ty: intern::SimpleType::ComptimeInt,
+            } => {
+                // This is a type variable.
+            }
+            intern::Key::SimpleType { .. }
+            | intern::Key::PointerType { .. }
+            | intern::Key::ArrayType { .. }
+            | intern::Key::FunctionType { .. }
+            | intern::Key::StructType { .. } => {
+                // This is a real type.
+            }
+            _ => unreachable!(),
+        }
 
         todo!()
     }

src/ast2/internable.rs

@@ -0,0 +1,34 @@
+use super::*;
+use core::hash::Hash;
+use std::hash::Hasher;
+
+// Types implementing this trait can be stored in the internpool.
+trait KeyTrait: Hash + Eq {
+    const TAG: Tag;
+    fn serialise(self, pool: &mut InternPool);
+    fn deserialise(index: Index, pool: &mut InternPool) -> Self;
+}
+
+impl KeyTrait for String {
+    const TAG: Tag = Tag::String;
+    fn serialise(self, pool: &mut InternPool) {
+        todo!()
+    }
+
+    fn deserialise(index: Index, pool: &mut InternPool) -> Self {
+        // let mut hasher = std::hash::DefaultHasher::new();
+        // core::any::TypeId::of::<Self>().hash(&mut hasher);
+        // let tag = hasher.finish() as u32;
+        let item = pool.get_item(index).unwrap();
+        assert_eq!(item.tag, Self::TAG);
+
+        let start = pool.words[item.idx()] as usize;
+        let len = pool.words[item.idx() + 1] as usize;
+        let str = unsafe {
+            let bytes = &pool.strings[start..start + len];
+            std::str::from_utf8_unchecked(bytes)
+        };
+
+        str.to_owned()
+    }
+}