refactored typedef

nac3core/rustfmt.toml

@@ -0,0 +1 @@
+ use_small_heuristics = "Max"

nac3core/src/typecheck/function_check.rs

@@ -32,7 +32,7 @@ impl<'a> Inferencer<'a> {
         // there are some cases where the custom field is None
         if let Some(ty) = &expr.custom {
             let ty = self.unifier.get_ty(*ty);
-            let ty = ty.as_ref().borrow();
+            let ty = ty.as_ref();
             if !ty.is_concrete() {
                 return Err(format!(
                     "expected concrete type at {} but got {}",

nac3core/src/typecheck/type_inferencer/mod.rs

@@ -54,17 +54,11 @@ impl<'a> fold::Fold<()> for Inferencer<'a> {
     fn fold_stmt(&mut self, node: ast::Stmt<()>) -> Result<ast::Stmt<Self::TargetU>, Self::Error> {
         let stmt = match node.node {
             // we don't want fold over type annotation
-            ast::StmtKind::AnnAssign {
+            ast::StmtKind::AnnAssign { target, annotation, value, simple } => {
-                target,
-                annotation,
-                value,
-                simple,
-            } => {
                 let target = Box::new(fold::fold_expr(self, *target)?);
                 let value = if let Some(v) = value {
                     let ty = Box::new(fold::fold_expr(self, *v)?);
-                    self.unifier
+                    self.unifier.unify(target.custom.unwrap(), ty.custom.unwrap())?;
-                        .unify(target.custom.unwrap(), ty.custom.unwrap())?;
                     Some(ty)
                 } else {
                     None
@@ -73,37 +67,27 @@ impl<'a> fold::Fold<()> for Inferencer<'a> {
                     .resolver
                     .parse_type_name(annotation.as_ref())
                     .ok_or_else(|| "cannot parse type name".to_string())?;
-                self.unifier
+                self.unifier.unify(annotation_type, target.custom.unwrap())?;
-                    .unify(annotation_type, target.custom.unwrap())?;
                 let annotation = Box::new(NaiveFolder().fold_expr(*annotation)?);
                 Located {
                     location: node.location,
                     custom: None,
-                    node: ast::StmtKind::AnnAssign {
+                    node: ast::StmtKind::AnnAssign { target, annotation, value, simple },
-                        target,
-                        annotation,
-                        value,
-                        simple,
-                    },
                 }
             }
             _ => fold::fold_stmt(self, node)?,
         };
         match &stmt.node {
             ast::StmtKind::For { target, iter, .. } => {
-                let list = self.unifier.add_ty(TypeEnum::TList {
+                let list = self.unifier.add_ty(TypeEnum::TList { ty: target.custom.unwrap() });
-                    ty: target.custom.unwrap(),
-                });
                 self.unifier.unify(list, iter.custom.unwrap())?;
             }
             ast::StmtKind::If { test, .. } | ast::StmtKind::While { test, .. } => {
-                self.unifier
+                self.unifier.unify(test.custom.unwrap(), self.primitives.bool)?;
-                    .unify(test.custom.unwrap(), self.primitives.bool)?;
             }
             ast::StmtKind::Assign { targets, value, .. } => {
                 for target in targets.iter() {
-                    self.unifier
+                    self.unifier.unify(target.custom.unwrap(), value.custom.unwrap())?;
-                        .unify(target.custom.unwrap(), value.custom.unwrap())?;
                 }
             }
             ast::StmtKind::AnnAssign { .. } | ast::StmtKind::Expr { .. } => {}
@@ -127,11 +111,7 @@ impl<'a> fold::Fold<()> for Inferencer<'a> {
 
     fn fold_expr(&mut self, node: ast::Expr<()>) -> Result<ast::Expr<Self::TargetU>, Self::Error> {
         let expr = match node.node {
-            ast::ExprKind::Call {
+            ast::ExprKind::Call { func, args, keywords } => {
-                func,
-                args,
-                keywords,
-            } => {
                 return self.fold_call(node.location, *func, args, keywords);
             }
             ast::ExprKind::Lambda { args, body } => {
@@ -147,19 +127,15 @@ impl<'a> fold::Fold<()> for Inferencer<'a> {
             ast::ExprKind::Name { id, .. } => Some(self.infer_identifier(id)?),
             ast::ExprKind::List { elts, .. } => Some(self.infer_list(elts)?),
             ast::ExprKind::Tuple { elts, .. } => Some(self.infer_tuple(elts)?),
-            ast::ExprKind::Attribute {
+            ast::ExprKind::Attribute { value, attr, ctx: _ } => {
-                value,
+                Some(self.infer_attribute(value, attr)?)
-                attr,
+            }
-                ctx: _,
-            } => Some(self.infer_attribute(value, attr)?),
             ast::ExprKind::BoolOp { values, .. } => Some(self.infer_bool_ops(values)?),
             ast::ExprKind::BinOp { left, op, right } => Some(self.infer_bin_ops(left, op, right)?),
             ast::ExprKind::UnaryOp { op, operand } => Some(self.infer_unary_ops(op, operand)?),
-            ast::ExprKind::Compare {
+            ast::ExprKind::Compare { left, ops, comparators } => {
-                left,
+                Some(self.infer_compare(left, ops, comparators)?)
-                ops,
+            }
-                comparators,
-            } => Some(self.infer_compare(left, ops, comparators)?),
             ast::ExprKind::Subscript { value, slice, .. } => {
                 Some(self.infer_subscript(value.as_ref(), slice.as_ref())?)
             }
@@ -172,11 +148,7 @@ impl<'a> fold::Fold<()> for Inferencer<'a> {
             ast::ExprKind::Slice { .. } => None, // we don't need it for slice
             _ => return Err("not supported yet".into()),
         };
-        Ok(ast::Expr {
+        Ok(ast::Expr { custom, location: expr.location, node: expr.node })
-            custom,
-            location: expr.location,
-            node: expr.node,
-        })
     }
 }
 
@@ -196,16 +168,12 @@ impl<'a> Inferencer<'a> {
         params: Vec<Type>,
         ret: Type,
     ) -> InferenceResult {
-        let call = Rc::new(Call {
+        let call =
-            posargs: params,
+            Rc::new(Call { posargs: params, kwargs: HashMap::new(), ret, fun: RefCell::new(None) });
-            kwargs: HashMap::new(),
-            ret,
-            fun: RefCell::new(None),
-        });
         self.calls.push(call.clone());
-        let call = self.unifier.add_ty(TypeEnum::TCall { calls: vec![call] });
+        let call = self.unifier.add_ty(TypeEnum::TCall(vec![call].into()));
         let fields = once((method, call)).collect();
-        let record = self.unifier.add_ty(TypeEnum::TRecord { fields });
+        let record = self.unifier.add_record(fields);
         self.constrain(obj, record)?;
         Ok(ret)
     }
@@ -248,11 +216,7 @@ impl<'a> Inferencer<'a> {
         let fun = FunSignature {
             args: fn_args
                 .iter()
-                .map(|(k, ty)| FuncArg {
+                .map(|(k, ty)| FuncArg { name: k.clone(), ty: *ty, is_optional: false })
-                    name: k.clone(),
-                    ty: *ty,
-                    is_optional: false,
-                })
                 .collect(),
             ret,
             vars: Default::default(),
@@ -266,10 +230,7 @@ impl<'a> Inferencer<'a> {
         }
         Ok(Located {
             location,
-            node: ExprKind::Lambda {
+            node: ExprKind::Lambda { args: args.into(), body: body.into() },
-                args: args.into(),
-                body: body.into(),
-            },
             custom: Some(self.unifier.add_ty(TypeEnum::TFunc(fun))),
         })
     }
@@ -282,7 +243,7 @@ impl<'a> Inferencer<'a> {
     ) -> Result<ast::Expr<Option<Type>>, String> {
         if generators.len() != 1 {
             return Err(
-                "Only 1 generator statement for list comprehension is supported.".to_string(),
+                "Only 1 generator statement for list comprehension is supported.".to_string()
             );
         }
         let variable_mapping = self.variable_mapping.clone();
@@ -309,22 +270,16 @@ impl<'a> Inferencer<'a> {
 
         // iter should be a list of targets...
         // actually it should be an iterator of targets, but we don't have iter type for now
-        let list = new_context.unifier.add_ty(TypeEnum::TList {
+        let list = new_context.unifier.add_ty(TypeEnum::TList { ty: target.custom.unwrap() });
-            ty: target.custom.unwrap(),
-        });
         new_context.unifier.unify(iter.custom.unwrap(), list)?;
         // if conditions should be bool
         for v in ifs.iter() {
-            new_context
+            new_context.unifier.unify(v.custom.unwrap(), new_context.primitives.bool)?;
-                .unifier
-                .unify(v.custom.unwrap(), new_context.primitives.bool)?;
         }
 
         Ok(Located {
             location,
-            custom: Some(new_context.unifier.add_ty(TypeEnum::TList {
+            custom: Some(new_context.unifier.add_ty(TypeEnum::TList { ty: elt.custom.unwrap() })),
-                ty: elt.custom.unwrap(),
-            })),
             node: ExprKind::ListComp {
                 elt: Box::new(elt),
                 generators: vec![ast::Comprehension {
@@ -344,77 +299,68 @@ impl<'a> Inferencer<'a> {
         mut args: Vec<ast::Expr<()>>,
         keywords: Vec<Located<ast::KeywordData>>,
     ) -> Result<ast::Expr<Option<Type>>, String> {
-        let func = if let Located {
+        let func =
-            location: func_location,
+            if let Located { location: func_location, custom, node: ExprKind::Name { id, ctx } } =
-            custom,
+                func
-            node: ExprKind::Name { id, ctx },
+            {
-        } = func
+                // handle special functions that cannot be typed in the usual way...
-        {
+                if id == "virtual" {
-            // handle special functions that cannot be typed in the usual way...
+                    if args.is_empty() || args.len() > 2 || !keywords.is_empty() {
-            if id == "virtual" {
+                        return Err(
-                if args.is_empty() || args.len() > 2 || !keywords.is_empty() {
+                            "`virtual` can only accept 1/2 positional arguments.".to_string()
-                    return Err("`virtual` can only accept 1/2 positional arguments.".to_string());
+                        );
-                }
-                let arg0 = self.fold_expr(args.remove(0))?;
-                let ty = if let Some(arg) = args.pop() {
-                    self.resolver
-                        .parse_type_name(&arg)
-                        .ok_or_else(|| "error parsing type".to_string())?
-                } else {
-                    self.unifier.get_fresh_var().0
-                };
-                let custom = Some(self.unifier.add_ty(TypeEnum::TVirtual { ty }));
-                return Ok(Located {
-                    location,
-                    custom,
-                    node: ExprKind::Call {
-                        func: Box::new(Located {
-                            custom: None,
-                            location: func.location,
-                            node: ExprKind::Name { id, ctx },
-                        }),
-                        args: vec![arg0],
-                        keywords: vec![],
-                    },
-                });
-            }
-            // int64 is special because its argument can be a constant larger than int32
-            if id == "int64" && args.len() == 1 {
-                if let ExprKind::Constant {
-                    value: ast::Constant::Int(val),
-                    kind,
-                } = &args[0].node
-                {
-                    let int64: Result<i64, _> = val.try_into();
-                    let custom;
-                    if int64.is_ok() {
-                        custom = Some(self.primitives.int64);
-                    } else {
-                        return Err("Integer out of bound".into());
                     }
+                    let arg0 = self.fold_expr(args.remove(0))?;
+                    let ty = if let Some(arg) = args.pop() {
+                        self.resolver
+                            .parse_type_name(&arg)
+                            .ok_or_else(|| "error parsing type".to_string())?
+                    } else {
+                        self.unifier.get_fresh_var().0
+                    };
+                    let custom = Some(self.unifier.add_ty(TypeEnum::TVirtual { ty }));
                     return Ok(Located {
-                        location: args[0].location,
+                        location,
                         custom,
-                        node: ExprKind::Constant {
+                        node: ExprKind::Call {
-                            value: ast::Constant::Int(val.clone()),
+                            func: Box::new(Located {
-                            kind: kind.clone(),
+                                custom: None,
+                                location: func.location,
+                                node: ExprKind::Name { id, ctx },
+                            }),
+                            args: vec![arg0],
+                            keywords: vec![],
                         },
                     });
                 }
-            }
+                // int64 is special because its argument can be a constant larger than int32
-            Located {
+                if id == "int64" && args.len() == 1 {
-                location: func_location,
+                    if let ExprKind::Constant { value: ast::Constant::Int(val), kind } =
-                custom,
+                        &args[0].node
-                node: ExprKind::Name { id, ctx },
+                    {
-            }
+                        let int64: Result<i64, _> = val.try_into();
-        } else {
+                        let custom;
-            func
+                        if int64.is_ok() {
-        };
+                            custom = Some(self.primitives.int64);
+                        } else {
+                            return Err("Integer out of bound".into());
+                        }
+                        return Ok(Located {
+                            location: args[0].location,
+                            custom,
+                            node: ExprKind::Constant {
+                                value: ast::Constant::Int(val.clone()),
+                                kind: kind.clone(),
+                            },
+                        });
+                    }
+                }
+                Located { location: func_location, custom, node: ExprKind::Name { id, ctx } }
+            } else {
+                func
+            };
         let func = Box::new(self.fold_expr(func)?);
-        let args = args
+        let args = args.into_iter().map(|v| self.fold_expr(v)).collect::<Result<Vec<_>, _>>()?;
-            .into_iter()
-            .map(|v| self.fold_expr(v))
-            .collect::<Result<Vec<_>, _>>()?;
         let keywords = keywords
             .into_iter()
             .map(|v| fold::fold_keyword(self, v))
@@ -430,18 +376,10 @@ impl<'a> Inferencer<'a> {
             ret,
         });
         self.calls.push(call.clone());
-        let call = self.unifier.add_ty(TypeEnum::TCall { calls: vec![call] });
+        let call = self.unifier.add_ty(TypeEnum::TCall(vec![call].into()));
         self.unifier.unify(func.custom.unwrap(), call)?;
 
-        Ok(Located {
+        Ok(Located { location, custom: Some(ret), node: ExprKind::Call { func, args, keywords } })
-            location,
-            custom: Some(ret),
-            node: ExprKind::Call {
-                func,
-                args,
-                keywords,
-            },
-        })
     }
 
     fn infer_identifier(&mut self, id: &str) -> InferenceResult {
@@ -493,7 +431,7 @@ impl<'a> Inferencer<'a> {
     fn infer_attribute(&mut self, value: &ast::Expr<Option<Type>>, attr: &str) -> InferenceResult {
         let (attr_ty, _) = self.unifier.get_fresh_var();
         let fields = once((attr.to_string(), attr_ty)).collect();
-        let record = self.unifier.add_ty(TypeEnum::TRecord { fields });
+        let record = self.unifier.add_record(fields);
         self.constrain(value.custom.unwrap(), record)?;
         Ok(attr_ty)
     }
@@ -540,9 +478,8 @@ impl<'a> Inferencer<'a> {
     ) -> InferenceResult {
         let boolean = self.primitives.bool;
         for (a, b, c) in izip!(once(left).chain(comparators), comparators, ops) {
-            let method = comparison_name(c)
+            let method =
-                .ok_or_else(|| "unsupported comparator".to_string())?
+                comparison_name(c).ok_or_else(|| "unsupported comparator".to_string())?.to_string();
-                .to_string();
             self.build_method_call(method, a.custom.unwrap(), vec![b.custom.unwrap()], boolean)?;
         }
         Ok(boolean)
@@ -556,26 +493,18 @@ impl<'a> Inferencer<'a> {
         let ty = self.unifier.get_fresh_var().0;
         match &slice.node {
             ast::ExprKind::Slice { lower, upper, step } => {
-                for v in [lower.as_ref(), upper.as_ref(), step.as_ref()]
+                for v in [lower.as_ref(), upper.as_ref(), step.as_ref()].iter().flatten() {
-                    .iter()
-                    .flatten()
-                {
                     self.constrain(v.custom.unwrap(), self.primitives.int32)?;
                 }
                 let list = self.unifier.add_ty(TypeEnum::TList { ty });
                 self.constrain(value.custom.unwrap(), list)?;
                 Ok(list)
             }
-            ast::ExprKind::Constant {
+            ast::ExprKind::Constant { value: ast::Constant::Int(val), .. } => {
-                value: ast::Constant::Int(val),
-                ..
-            } => {
                 // the index is a constant, so value can be a sequence.
-                let ind: i32 = val
+                let ind: i32 = val.try_into().map_err(|_| "Index must be int32".to_string())?;
-                    .try_into()
-                    .map_err(|_| "Index must be int32".to_string())?;
                 let map = once((ind, ty)).collect();
-                let seq = self.unifier.add_ty(TypeEnum::TSeq { map });
+                let seq = self.unifier.add_sequence(map);
                 self.constrain(value.custom.unwrap(), seq)?;
                 Ok(ty)
             }

nac3core/src/typecheck/typedef/mod.rs

@@ -1,4 +1,5 @@
-use itertools::Itertools;
+use itertools::{chain, zip, Itertools};
+use std::borrow::Cow;
 use std::cell::RefCell;
 use std::collections::HashMap;
 use std::iter::once;
@@ -12,9 +13,6 @@ mod test;
 /// Handle for a type, implementated as a key in the unification table.
 pub type Type = UnificationKey;
 
-#[derive(Clone)]
-pub struct TypeCell(Rc<RefCell<TypeEnum>>);
-
 pub type Mapping<K, V = Type> = HashMap<K, V>;
 type VarMap = Mapping<u32>;
 
@@ -40,16 +38,20 @@ pub struct FunSignature {
     pub vars: VarMap,
 }
 
-// We use a lot of `Rc`/`RefCell`s here as we want to simplify our code.
+#[derive(Clone)]
-// We may not really need so much `Rc`s, but we would have to do complicated
+pub enum TypeVarMeta {
-// stuffs otherwise.
+    Generic,
+    Sequence(RefCell<Mapping<i32>>),
+    Record(RefCell<Mapping<String>>),
+}
+
 #[derive(Clone)]
 pub enum TypeEnum {
     TVar {
         id: u32,
-    },
+        meta: TypeVarMeta,
-    TSeq {
+        // empty indicates no restriction
-        map: Mapping<i32>,
+        range: RefCell<Vec<Type>>,
     },
     TTuple {
         ty: Vec<Type>,
@@ -57,9 +59,6 @@ pub enum TypeEnum {
     TList {
         ty: Type,
     },
-    TRecord {
-        fields: Mapping<String>,
-    },
     TObj {
         obj_id: usize,
         fields: Mapping<String>,
@@ -68,33 +67,16 @@ pub enum TypeEnum {
     TVirtual {
         ty: Type,
     },
-    TCall {
+    TCall(RefCell<Vec<Rc<Call>>>),
-        calls: Vec<Rc<Call>>,
-    },
     TFunc(FunSignature),
 }
 
-// Order:
-// TVar
-// |--> TSeq
-// |   |--> TTuple
-// |   `--> TList
-// |--> TRecord
-// |   |--> TObj
-// |   `--> TVirtual
-// `--> TCall
-//     `--> TFunc
-
 impl TypeEnum {
     pub fn get_type_name(&self) -> &'static str {
-        // this function is for debugging only...
-        // a proper to_str implementation requires the context
         match self {
             TypeEnum::TVar { .. } => "TVar",
-            TypeEnum::TSeq { .. } => "TSeq",
             TypeEnum::TTuple { .. } => "TTuple",
             TypeEnum::TList { .. } => "TList",
-            TypeEnum::TRecord { .. } => "TRecord",
             TypeEnum::TObj { .. } => "TObj",
             TypeEnum::TVirtual { .. } => "TVirtual",
             TypeEnum::TCall { .. } => "TCall",
@@ -103,176 +85,168 @@ impl TypeEnum {
     }
 
     pub fn is_concrete(&self) -> bool {
-        matches!(
+        !matches!(self, TypeEnum::TVar { .. })
-            self,
-            TypeEnum::TTuple { .. }
-                | TypeEnum::TList { .. }
-                | TypeEnum::TObj { .. }
-                | TypeEnum::TVirtual { .. }
-                | TypeEnum::TFunc { .. }
-        )
     }
 }
 
 pub struct Unifier {
-    unification_table: UnificationTable<Rc<RefCell<TypeEnum>>>,
+    unification_table: UnificationTable<Rc<TypeEnum>>,
     var_id: u32,
 }
 
 impl Unifier {
     /// Get an empty unifier
     pub fn new() -> Unifier {
-        Unifier {
+        Unifier { unification_table: UnificationTable::new(), var_id: 0 }
-            unification_table: UnificationTable::new(),
-            var_id: 0,
-        }
     }
 
     /// Register a type to the unifier.
     /// Returns a key in the unification_table.
     pub fn add_ty(&mut self, a: TypeEnum) -> Type {
-        self.unification_table.new_key(Rc::new(a.into()))
+        self.unification_table.new_key(Rc::new(a))
+    }
+
+    pub fn add_record(&mut self, fields: Mapping<String>) -> Type {
+        let id = self.var_id + 1;
+        self.var_id += 1;
+        self.add_ty(TypeEnum::TVar {
+            id,
+            range: vec![].into(),
+            meta: TypeVarMeta::Record(fields.into()),
+        })
+    }
+
+    pub fn add_sequence(&mut self, sequence: Mapping<i32>) -> Type {
+        let id = self.var_id + 1;
+        self.var_id += 1;
+        self.add_ty(TypeEnum::TVar {
+            id,
+            range: vec![].into(),
+            meta: TypeVarMeta::Sequence(sequence.into()),
+        })
     }
 
     /// Get the TypeEnum of a type.
-    pub fn get_ty(&mut self, a: Type) -> Rc<RefCell<TypeEnum>> {
+    pub fn get_ty(&mut self, a: Type) -> Rc<TypeEnum> {
         self.unification_table.probe_value(a).clone()
     }
 
-    /// Unify two types, i.e. a = b.
+    pub fn get_fresh_var(&mut self) -> (Type, u32) {
-    pub fn unify(&mut self, a: Type, b: Type) -> Result<(), String> {
+        self.get_fresh_var_with_range(&[])
-        self.unify_impl(a, b, false)
     }
 
     /// Get a fresh type variable.
-    pub fn get_fresh_var(&mut self) -> (Type, u32) {
+    pub fn get_fresh_var_with_range(&mut self, range: &[Type]) -> (Type, u32) {
         let id = self.var_id + 1;
         self.var_id += 1;
-        (self.add_ty(TypeEnum::TVar { id }), id)
+        let range = range.to_vec().into();
+        (self.add_ty(TypeEnum::TVar { id, range, meta: TypeVarMeta::Generic }), id)
     }
 
-    /// Get string representation of the type
+    pub fn unify(&mut self, a: Type, b: Type) -> Result<(), String> {
-    pub fn stringify<F, G>(&mut self, ty: Type, obj_to_name: &mut F, var_to_name: &mut G) -> String
+        if self.unification_table.unioned(a, b) {
-    where
+            Ok(())
-        F: FnMut(usize) -> String,
+        } else {
-        G: FnMut(u32) -> String,
+            self.unify_impl(a, b, false)
-    {
-        let ty = self.unification_table.probe_value(ty).clone();
-        let ty = ty.as_ref().borrow();
-        match &*ty {
-            TypeEnum::TVar { id } => var_to_name(*id),
-            TypeEnum::TSeq { map } => {
-                let mut fields = map.iter().map(|(k, v)| {
-                    format!("{}={}", k, self.stringify(*v, obj_to_name, var_to_name))
-                });
-                format!("seq[{}]", fields.join(", "))
-            }
-            TypeEnum::TTuple { ty } => {
-                let mut fields = ty
-                    .iter()
-                    .map(|v| self.stringify(*v, obj_to_name, var_to_name));
-                format!("tuple[{}]", fields.join(", "))
-            }
-            TypeEnum::TList { ty } => {
-                format!("list[{}]", self.stringify(*ty, obj_to_name, var_to_name))
-            }
-            TypeEnum::TVirtual { ty } => {
-                format!("virtual[{}]", self.stringify(*ty, obj_to_name, var_to_name))
-            }
-            TypeEnum::TRecord { fields } => {
-                let mut fields = fields.iter().map(|(k, v)| {
-                    format!("{}={}", k, self.stringify(*v, obj_to_name, var_to_name))
-                });
-                format!("record[{}]", fields.join(", "))
-            }
-            TypeEnum::TObj { obj_id, params, .. } => {
-                let name = obj_to_name(*obj_id);
-                if !params.is_empty() {
-                    let mut params = params
-                        .values()
-                        .map(|v| self.stringify(*v, obj_to_name, var_to_name));
-                    format!("{}[{}]", name, params.join(", "))
-                } else {
-                    name
-                }
-            }
-            TypeEnum::TCall { .. } => "call".to_owned(),
-            TypeEnum::TFunc(signature) => {
-                let params = signature
-                    .args
-                    .iter()
-                    .map(|arg| {
-                        format!(
-                            "{}={}",
-                            arg.name,
-                            self.stringify(arg.ty, obj_to_name, var_to_name)
-                        )
-                    })
-                    .join(", ");
-                let ret = self.stringify(signature.ret, obj_to_name, var_to_name);
-                format!("fn[[{}], {}]", params, ret)
-            }
         }
     }
 
     fn unify_impl(&mut self, a: Type, b: Type, swapped: bool) -> Result<(), String> {
         use TypeEnum::*;
-        let (ty_a_cell, ty_b_cell) = {
+        use TypeVarMeta::*;
-            if self.unification_table.unioned(a, b) {
+        let (ty_a, ty_b) = {
-                return Ok(());
-            }
             (
                 self.unification_table.probe_value(a).clone(),
                 self.unification_table.probe_value(b).clone(),
             )
         };
-
-        let (ty_a, ty_b) = { (ty_a_cell.borrow(), ty_b_cell.borrow()) };
-
         match (&*ty_a, &*ty_b) {
-            (TypeEnum::TVar { .. }, _) => {
+            (TVar { meta: meta1, range: range1, .. }, TVar { meta: meta2, range: range2, .. }) => {
                 self.occur_check(a, b)?;
-                self.set_a_to_b(a, b);
+                self.occur_check(b, a)?;
-            }
+                match (meta1, meta2) {
-            (TSeq { map: map1 }, TSeq { .. }) => {
+                    (Generic, _) => {}
-                self.occur_check(a, b)?;
+                    (_, Generic) => {
-                drop(ty_b);
+                        return self.unify_impl(b, a, true);
-                if let TypeEnum::TSeq { map: map2 } = &mut *ty_b_cell.as_ref().borrow_mut() {
+                    }
-                    // unify them to map2
+                    (Record(fields1), Record(fields2)) => {
-                    for (key, value) in map1.iter() {
+                        let mut fields2 = fields2.borrow_mut();
-                        if let Some(ty) = map2.get(key) {
+                        for (key, value) in fields1.borrow().iter() {
-                            self.unify(*ty, *value)?;
+                            if let Some(ty) = fields2.get(key) {
-                        } else {
+                                self.unify(*ty, *value)?;
-                            map2.insert(*key, *value);
+                            } else {
+                                fields2.insert(key.clone(), *value);
+                            }
                         }
                     }
-                } else {
+                    (Sequence(map1), Sequence(map2)) => {
-                    unreachable!()
+                        let mut map2 = map2.borrow_mut();
+                        for (key, value) in map1.borrow().iter() {
+                            if let Some(ty) = map2.get(key) {
+                                self.unify(*ty, *value)?;
+                            } else {
+                                map2.insert(*key, *value);
+                            }
+                        }
+                    }
+                    _ => {
+                        return Err("Incompatible".to_string());
+                    }
+                }
+                let range1 = range1.borrow();
+                // new range is the intersection of them
+                // empty range indicates no constraint
+                if !range1.is_empty() {
+                    let old_range2 = range2.take();
+                    let mut range2 = range2.borrow_mut();
+                    if old_range2.is_empty() {
+                        range2.extend_from_slice(&range1);
+                    }
+                    for v1 in old_range2.iter() {
+                        for v2 in range1.iter() {
+                            if !self.shape_match(*v1, *v2) {
+                                continue;
+                            }
+                            self.unify(*v1, *v2)?;
+                            range2.push(*v2);
+                        }
+                    }
+                    if range2.is_empty() {
+                        return Err(
+                            "cannot unify type variables with incompatible value range".to_string()
+                        );
+                    }
                 }
                 self.set_a_to_b(a, b);
             }
-            (TSeq { map: map1 }, TTuple { ty: types }) => {
+            (TVar { meta: Generic, id, range, .. }, _) => {
                 self.occur_check(a, b)?;
-                let len = types.len() as i32;
+                self.check_var_range(*id, b, &range.borrow())?;
-                for (k, v) in map1.iter() {
+                self.set_a_to_b(a, b);
+            }
+            (TVar { meta: Sequence(map), id, range, .. }, TTuple { ty }) => {
+                self.occur_check(a, b)?;
+                let len = ty.len() as i32;
+                for (k, v) in map.borrow().iter() {
                     // handle negative index
                     let ind = if *k < 0 { len + *k } else { *k };
                     if ind >= len || ind < 0 {
                         return Err(format!(
                             "Tuple index out of range. (Length: {}, Index: {})",
-                            types.len(),
+                            len, k
-                            k
                         ));
                     }
-                    self.unify(*v, types[ind as usize])?;
+                    self.unify(*v, ty[ind as usize])?;
                 }
+                self.check_var_range(*id, b, &range.borrow())?;
                 self.set_a_to_b(a, b);
             }
-            (TSeq { map: map1 }, TList { ty }) => {
+            (TVar { meta: Sequence(map), id, range, .. }, TList { ty }) => {
                 self.occur_check(a, b)?;
-                for v in map1.values() {
+                for v in map.borrow().values() {
                     self.unify(*v, *ty)?;
                 }
+                self.check_var_range(*id, b, &range.borrow())?;
                 self.set_a_to_b(a, b);
             }
             (TTuple { ty: ty1 }, TTuple { ty: ty2 }) => {
@@ -292,59 +266,32 @@ impl Unifier {
                 self.unify(*ty1, *ty2)?;
                 self.set_a_to_b(a, b);
             }
-            (TRecord { fields: fields1 }, TRecord { .. }) => {
+            (TVar { meta: Record(map), id, range, .. }, TObj { fields, .. }) => {
                 self.occur_check(a, b)?;
-                drop(ty_b);
+                for (k, v) in map.borrow().iter() {
-                if let TypeEnum::TRecord { fields: fields2 } = &mut *ty_b_cell.as_ref().borrow_mut()
+                    if let Some(ty) = fields.get(k) {
-                {
+                        self.unify(*ty, *v)?;
-                    for (key, value) in fields1.iter() {
-                        if let Some(ty) = fields2.get(key) {
-                            self.unify(*ty, *value)?;
-                        } else {
-                            fields2.insert(key.clone(), *value);
-                        }
-                    }
-                } else {
-                    unreachable!()
-                }
-                self.set_a_to_b(a, b);
-            }
-            (
-                TRecord { fields: fields1 },
-                TObj {
-                    fields: fields2, ..
-                },
-            ) => {
-                self.occur_check(a, b)?;
-                for (key, value) in fields1.iter() {
-                    if let Some(ty) = fields2.get(key) {
-                        self.unify(*ty, *value)?;
                     } else {
-                        return Err(format!("No such attribute {}", key));
+                        return Err(format!("No such attribute {}", k));
                     }
                 }
+                self.check_var_range(*id, b, &range.borrow())?;
                 self.set_a_to_b(a, b);
             }
-            (TRecord { .. }, TVirtual { ty }) => {
+            (TVar { meta: Record(_), id, range, .. }, TVirtual { ty }) => {
+                // TODO: look at this rule
                 self.occur_check(a, b)?;
+                self.check_var_range(*id, b, &range.borrow())?;
                 self.unify(a, *ty)?;
             }
             (
-                TObj {
+                TObj { obj_id: id1, params: params1, .. },
-                    obj_id: id1,
+                TObj { obj_id: id2, params: params2, .. },
-                    params: params1,
-                    ..
-                },
-                TObj {
-                    obj_id: id2,
-                    params: params2,
-                    ..
-                },
             ) => {
                 if id1 != id2 {
                     return Err(format!("Cannot unify objects with ID {} and {}", id1, id2));
                 }
-                for (x, y) in params1.values().zip(params2.values()) {
+                for (x, y) in zip(params1.values(), params2.values()) {
                     self.unify(*x, *y)?;
                 }
                 self.set_a_to_b(a, b);
@@ -353,16 +300,10 @@ impl Unifier {
                 self.unify(*ty1, *ty2)?;
                 self.set_a_to_b(a, b);
             }
-            (TCall { calls: c1 }, TCall { .. }) => {
+            (TCall(calls1), TCall(calls2)) => {
-                drop(ty_b);
+                calls2.borrow_mut().extend_from_slice(&calls1.borrow());
-                if let TypeEnum::TCall { calls: c2 } = &mut *ty_b_cell.as_ref().borrow_mut() {
-                    c2.extend(c1.iter().cloned());
-                } else {
-                    unreachable!()
-                }
-                self.set_a_to_b(a, b);
             }
-            (TCall { calls }, TFunc(signature)) => {
+            (TCall(calls), TFunc(signature)) => {
                 self.occur_check(a, b)?;
                 let required: Vec<String> = signature
                     .args
@@ -371,29 +312,20 @@ impl Unifier {
                     .map(|v| v.name.clone())
                     .rev()
                     .collect();
-                for c in calls {
+                for c in calls.borrow().iter() {
-                    let Call {
+                    let Call { posargs, kwargs, ret, fun } = c.as_ref();
-                        posargs,
-                        kwargs,
-                        ret,
-                        fun,
-                    } = c.as_ref();
                     let instantiated = self.instantiate_fun(b, signature);
                     let signature;
                     let r = self.get_ty(instantiated);
-                    let r = r.as_ref().borrow();
+                    let r = r.as_ref();
                     if let TypeEnum::TFunc(s) = &*r {
                         signature = s;
                     } else {
                         unreachable!();
                     }
                     let mut required = required.clone();
-                    let mut all_names: Vec<_> = signature
+                    let mut all_names: Vec<_> =
-                        .args
+                        signature.args.iter().map(|v| (v.name.clone(), v.ty)).rev().collect();
-                        .iter()
-                        .map(|v| (v.name.clone(), v.ty))
-                        .rev()
-                        .collect();
                     for (i, t) in posargs.iter().enumerate() {
                         if signature.args.len() <= i {
                             return Err("Too many arguments.".to_string());
@@ -451,6 +383,88 @@ impl Unifier {
         Ok(())
     }
 
+    /// Get string representation of the type
+    pub fn stringify<F, G>(&mut self, ty: Type, obj_to_name: &mut F, var_to_name: &mut G) -> String
+    where
+        F: FnMut(usize) -> String,
+        G: FnMut(u32) -> String,
+    {
+        use TypeVarMeta::*;
+        let ty = self.unification_table.probe_value(ty).clone();
+        match ty.as_ref() {
+            TypeEnum::TVar { id, meta: Generic, .. } => var_to_name(*id),
+            TypeEnum::TVar { meta: Sequence(map), .. } => {
+                let fields = map.borrow().iter().map(|(k, v)| {
+                    format!("{}={}", k, self.stringify(*v, obj_to_name, var_to_name))
+                }).join(", ");
+                format!("seq[{}]", fields)
+            }
+            TypeEnum::TVar { meta: Record(fields), .. } => {
+                let fields = fields.borrow().iter().map(|(k, v)| {
+                    format!("{}={}", k, self.stringify(*v, obj_to_name, var_to_name))
+                }).join(", ");
+                format!("record[{}]", fields)
+            }
+            TypeEnum::TTuple { ty } => {
+                let mut fields = ty
+                    .iter()
+                    .map(|v| self.stringify(*v, obj_to_name, var_to_name));
+                format!("tuple[{}]", fields.join(", "))
+            }
+            TypeEnum::TList { ty } => {
+                format!("list[{}]", self.stringify(*ty, obj_to_name, var_to_name))
+            }
+            TypeEnum::TVirtual { ty } => {
+                format!("virtual[{}]", self.stringify(*ty, obj_to_name, var_to_name))
+            }
+            TypeEnum::TObj { obj_id, params, .. } => {
+                let name = obj_to_name(*obj_id);
+                if !params.is_empty() {
+                    let mut params = params
+                        .values()
+                        .map(|v| self.stringify(*v, obj_to_name, var_to_name));
+                    format!("{}[{}]", name, params.join(", "))
+                } else {
+                    name
+                }
+            }
+            TypeEnum::TCall { .. } => "call".to_owned(),
+            TypeEnum::TFunc(signature) => {
+                let params = signature
+                    .args
+                    .iter()
+                    .map(|arg| {
+                        format!(
+                            "{}={}",
+                            arg.name,
+                            self.stringify(arg.ty, obj_to_name, var_to_name)
+                        )
+                    })
+                    .join(", ");
+                let ret = self.stringify(signature.ret, obj_to_name, var_to_name);
+                format!("fn[[{}], {}]", params, ret)
+            }
+        }
+    }
+
+    fn check_var_range(&mut self, id: u32, b: Type, range: &[Type]) -> Result<(), String> {
+        let mut in_range = range.is_empty();
+        for t in range.iter() {
+            if self.shape_match(*t, b) {
+                self.unify(*t, b)?;
+                in_range = true;
+            }
+        }
+        if !in_range {
+            return Err(format!(
+                "Cannot unify {} with {} due to incompatible value range",
+                id,
+                self.get_ty(b).get_type_name()
+            ));
+        }
+        Ok(())
+    }
+
     fn set_a_to_b(&mut self, a: Type, b: Type) {
         // unify a and b together, and set the value to b's value.
         let table = &mut self.unification_table;
@@ -460,77 +474,40 @@ impl Unifier {
     }
 
     fn incompatible_types(&self, a: &TypeEnum, b: &TypeEnum) -> Result<(), String> {
-        Err(format!(
+        Err(format!("Cannot unify {} with {}", a.get_type_name(), b.get_type_name()))
-            "Cannot unify {} with {}",
-            a.get_type_name(),
-            b.get_type_name()
-        ))
     }
 
-    fn occur_check(&mut self, a: Type, b: Type) -> Result<(), String> {
+    /// Instantiate a function if it hasn't been instntiated.
-        if self.unification_table.unioned(a, b) {
+    /// Returns Some(T) where T is the instantiated type.
-            return Err("Recursive type is prohibited.".to_owned());
+    /// Returns None if the function is already instantiated.
+    fn instantiate_fun(&mut self, ty: Type, fun: &FunSignature) -> Type {
+        let mut instantiated = false;
+        let mut vars = Vec::new();
+        for (k, v) in fun.vars.iter() {
+            if let TypeEnum::TVar { id, range, .. } =
+                self.unification_table.probe_value(*v).as_ref()
+            {
+                if k != id {
+                    instantiated = true;
+                    break;
+                }
+                // actually, if the first check succeeded, the function should be uninstatiated.
+                // The cloned values must be used and would not be wasted.
+                vars.push((*k, range.clone()));
+            } else {
+                instantiated = true;
+                break;
+            }
+        }
+        if instantiated {
+            ty
+        } else {
+            let mapping = vars
+                .into_iter()
+                .map(|(k, range)| (k, self.get_fresh_var_with_range(range.borrow().as_ref()).0))
+                .collect();
+            self.subst(ty, &mapping).unwrap_or(ty)
         }
-        let ty = self.unification_table.probe_value(b).clone();
-        let ty = ty.borrow();
-
-        match &*ty {
-            TypeEnum::TVar { .. } => {
-                // TODO: occur check for bounds...
-            }
-            TypeEnum::TSeq { map } => {
-                for t in map.values() {
-                    self.occur_check(a, *t)?;
-                }
-            }
-            TypeEnum::TTuple { ty } => {
-                for t in ty.iter() {
-                    self.occur_check(a, *t)?;
-                }
-            }
-            TypeEnum::TList { ty } | TypeEnum::TVirtual { ty } => {
-                self.occur_check(a, *ty)?;
-            }
-            TypeEnum::TRecord { fields } => {
-                for t in fields.values() {
-                    self.occur_check(a, *t)?;
-                }
-            }
-            TypeEnum::TObj { params: map, .. } => {
-                for t in map.values() {
-                    self.occur_check(a, *t)?;
-                }
-            }
-            TypeEnum::TCall { calls } => {
-                for t in calls
-                    .iter()
-                    .map(|call| {
-                        call.posargs
-                            .iter()
-                            .chain(call.kwargs.values())
-                            .chain(once(&call.ret))
-                    })
-                    .flatten()
-                {
-                    self.occur_check(a, *t)?;
-                }
-            }
-            TypeEnum::TFunc(FunSignature {
-                args,
-                ret,
-                vars: params,
-            }) => {
-                for t in args
-                    .iter()
-                    .map(|v| &v.ty)
-                    .chain(params.values())
-                    .chain(once(ret))
-                {
-                    self.occur_check(a, *t)?;
-                }
-            }
-        };
-        Ok(())
     }
 
     /// Substitute type variables within a type into other types.
@@ -538,48 +515,41 @@ impl Unifier {
     /// If this returns None, the result type would be the original type
     /// (no substitution has to be done).
     fn subst(&mut self, a: Type, mapping: &VarMap) -> Option<Type> {
-        let ty_cell = self.unification_table.probe_value(a).clone();
+        use TypeVarMeta::*;
-        let ty = ty_cell.borrow();
+        let ty = self.unification_table.probe_value(a).clone();
         // this function would only be called when we instantiate functions.
         // function type signature should ONLY contain concrete types and type
         // variables, i.e. things like TRecord, TCall should not occur, and we
         // should be safe to not implement the substitution for those variants.
         match &*ty {
-            TypeEnum::TVar { id } => mapping.get(&id).cloned(),
+            TypeEnum::TVar { id, meta: Generic, .. } => mapping.get(&id).cloned(),
-            TypeEnum::TSeq { map } => self
-                .subst_map(map, mapping)
-                .map(|m| self.add_ty(TypeEnum::TSeq { map: m })),
             TypeEnum::TTuple { ty } => {
-                let mut new_ty = None;
+                let mut new_ty = Cow::from(ty);
                 for (i, t) in ty.iter().enumerate() {
                     if let Some(t1) = self.subst(*t, mapping) {
-                        if new_ty.is_none() {
+                        new_ty.to_mut()[i] = t1;
-                            new_ty = Some(ty.clone());
-                        }
-                        new_ty.as_mut().unwrap()[i] = t1;
                     }
                 }
-                new_ty.map(|t| self.add_ty(TypeEnum::TTuple { ty: t }))
+                if matches!(new_ty, Cow::Owned(_)) {
+                    Some(self.add_ty(TypeEnum::TTuple { ty: new_ty.into_owned() }))
+                } else {
+                    None
+                }
             }
-            TypeEnum::TList { ty } => self
+            TypeEnum::TList { ty } => {
-                .subst(*ty, mapping)
+                self.subst(*ty, mapping).map(|t| self.add_ty(TypeEnum::TList { ty: t }))
-                .map(|t| self.add_ty(TypeEnum::TList { ty: t })),
+            }
-            TypeEnum::TVirtual { ty } => self
+            TypeEnum::TVirtual { ty } => {
-                .subst(*ty, mapping)
+                self.subst(*ty, mapping).map(|t| self.add_ty(TypeEnum::TVirtual { ty: t }))
-                .map(|t| self.add_ty(TypeEnum::TVirtual { ty: t })),
+            }
-            TypeEnum::TObj {
+            TypeEnum::TObj { obj_id, fields, params } => {
-                obj_id,
-                fields,
-                params,
-            } => {
                 // Type variables in field types must be present in the type parameter.
                 // If the mapping does not contain any type variables in the
                 // parameter list, we don't need to substitute the fields.
                 // This is also used to prevent infinite substitution...
                 let need_subst = params.values().any(|v| {
-                    let ty_cell = self.unification_table.probe_value(*v);
+                    let ty = self.unification_table.probe_value(*v);
-                    let ty = ty_cell.borrow();
+                    if let TypeEnum::TVar { id, .. } = ty.as_ref() {
-                    if let TypeEnum::TVar { id } = &*ty {
                         mapping.contains_key(&id)
                     } else {
                         false
@@ -587,50 +557,29 @@ impl Unifier {
                 });
                 if need_subst {
                     let obj_id = *obj_id;
-                    let params = self
+                    let params = self.subst_map(&params, mapping).unwrap_or_else(|| params.clone());
-                        .subst_map(&params, mapping)
+                    let fields = self.subst_map(&fields, mapping).unwrap_or_else(|| fields.clone());
-                        .unwrap_or_else(|| params.clone());
+                    Some(self.add_ty(TypeEnum::TObj { obj_id, params, fields }))
-                    let fields = self
-                        .subst_map(&fields, mapping)
-                        .unwrap_or_else(|| fields.clone());
-                    Some(self.add_ty(TypeEnum::TObj {
-                        obj_id,
-                        params,
-                        fields,
-                    }))
                 } else {
                     None
                 }
             }
-            TypeEnum::TFunc(FunSignature {
+            TypeEnum::TFunc(FunSignature { args, ret, vars: params }) => {
-                args,
-                ret,
-                vars: params,
-            }) => {
                 let new_params = self.subst_map(params, mapping);
                 let new_ret = self.subst(*ret, mapping);
-                let mut new_args = None;
+                let mut new_args = Cow::from(args);
                 for (i, t) in args.iter().enumerate() {
                     if let Some(t1) = self.subst(t.ty, mapping) {
-                        if new_args.is_none() {
+                        let mut t = t.clone();
-                            new_args = Some(args.clone());
+                        t.ty = t1;
-                        }
+                        new_args.to_mut()[i] = t;
-                        new_args.as_mut().unwrap()[i] = FuncArg {
-                            name: t.name.clone(),
-                            ty: t1,
-                            is_optional: t.is_optional,
-                        };
                     }
                 }
-                if new_params.is_some() || new_ret.is_some() || new_args.is_some() {
+                if new_params.is_some() || new_ret.is_some() || matches!(new_args, Cow::Owned(..)) {
                     let params = new_params.unwrap_or_else(|| params.clone());
                     let ret = new_ret.unwrap_or_else(|| *ret);
-                    let args = new_args.unwrap_or_else(|| args.clone());
+                    let args = new_args.into_owned();
-                    Some(self.add_ty(TypeEnum::TFunc(FunSignature {
+                    Some(self.add_ty(TypeEnum::TFunc(FunSignature { args, ret, vars: params })))
-                        args,
-                        ret,
-                        vars: params,
-                    })))
                 } else {
                     None
                 }
@@ -655,95 +604,73 @@ impl Unifier {
         map2
     }
 
-    /// Instantiate a function if it hasn't been instntiated.
+    fn occur_check(&mut self, a: Type, b: Type) -> Result<(), String> {
-    /// Returns Some(T) where T is the instantiated type.
+        use TypeVarMeta::*;
-    /// Returns None if the function is already instantiated.
+        if self.unification_table.unioned(a, b) {
-    fn instantiate_fun(&mut self, ty: Type, fun: &FunSignature) -> Type {
+            return Err("Recursive type is prohibited.".to_owned());
-        let mut instantiated = false;
+        }
-        for (k, v) in fun.vars.iter() {
+        let ty = self.unification_table.probe_value(b).clone();
-            if let TypeEnum::TVar { id } =
+
-                &*self.unification_table.probe_value(*v).as_ref().borrow()
+        match ty.as_ref() {
-            {
+            TypeEnum::TVar { meta: Generic, .. } => {}
-                if k != id {
+            TypeEnum::TVar { meta: Sequence(map), .. } => {
-                    instantiated = true;
+                for t in map.borrow().values() {
-                    break;
+                    self.occur_check(a, *t)?;
+                }
+            }
+            TypeEnum::TVar { meta: Record(map), .. } => {
+                for t in map.borrow().values() {
+                    self.occur_check(a, *t)?;
+                }
+            }
+            TypeEnum::TCall(calls) => {
+                for t in calls
+                    .borrow()
+                    .iter()
+                    .map(|call| chain!(call.posargs.iter(), call.kwargs.values(), once(&call.ret)))
+                    .flatten()
+                {
+                    self.occur_check(a, *t)?;
+                }
+            }
+            TypeEnum::TTuple { ty } => {
+                for t in ty.iter() {
+                    self.occur_check(a, *t)?;
+                }
+            }
+            TypeEnum::TList { ty } | TypeEnum::TVirtual { ty } => {
+                self.occur_check(a, *ty)?;
+            }
+            TypeEnum::TObj { params: map, .. } => {
+                for t in map.values() {
+                    self.occur_check(a, *t)?;
+                }
+            }
+            TypeEnum::TFunc(FunSignature { args, ret, vars: params }) => {
+                for t in chain!(args.iter().map(|v| &v.ty), params.values(), once(ret)) {
+                    self.occur_check(a, *t)?;
                 }
-            } else {
-                instantiated = true;
-                break;
             }
         }
-        if instantiated {
+        Ok(())
-            ty
-        } else {
-            let mapping = fun
-                .vars
-                .iter()
-                .map(|(k, _)| (*k, self.get_fresh_var().0))
-                .collect();
-            self.subst(ty, &mapping).unwrap_or(ty)
-        }
     }
 
-    /// Check whether two types are equal.
+    pub fn shape_match(&mut self, a: Type, b: Type) -> bool {
-    fn eq(&mut self, a: Type, b: Type) -> bool {
+        use TypeEnum::*;
-        if a == b {
+        let a = self.get_ty(a);
-            return true;
+        let b = self.get_ty(b);
-        }
+        match (a.as_ref(), b.as_ref()) {
-        let (ty_a, ty_b) = {
+            (TVar { .. }, _) => true,
-            let table = &mut self.unification_table;
+            (_, TVar { .. }) => true,
-            if table.unioned(a, b) {
+            (TTuple { ty: ty1 }, TTuple { ty: ty2 }) => {
-                return true;
-            }
-            (table.probe_value(a).clone(), table.probe_value(b).clone())
-        };
-
-        let ty_a = ty_a.borrow();
-        let ty_b = ty_b.borrow();
-
-        match (&*ty_a, &*ty_b) {
-            (TypeEnum::TVar { id: id1 }, TypeEnum::TVar { id: id2 }) => id1 == id2,
-            (TypeEnum::TSeq { map: map1 }, TypeEnum::TSeq { map: map2 }) => self.map_eq(map1, map2),
-            (TypeEnum::TTuple { ty: ty1 }, TypeEnum::TTuple { ty: ty2 }) => {
                 ty1.len() == ty2.len()
-                    && ty1.iter().zip(ty2.iter()).all(|(t1, t2)| self.eq(*t1, *t2))
+                    && zip(ty1.iter(), ty2.iter()).all(|(a, b)| self.shape_match(*a, *b))
             }
-            (TypeEnum::TList { ty: ty1 }, TypeEnum::TList { ty: ty2 })
+            (TList { ty: ty1 }, TList { ty: ty2 })
-            | (TypeEnum::TVirtual { ty: ty1 }, TypeEnum::TVirtual { ty: ty2 }) => {
+            | (TVirtual { ty: ty1 }, TVirtual { ty: ty2 }) => self.shape_match(*ty1, *ty2),
-                self.eq(*ty1, *ty2)
+            (TObj { obj_id: id1, .. }, TObj { obj_id: id2, .. }) => id1 == id2,
-            }
+            // don't deal with function shape for now
-            (TypeEnum::TRecord { fields: fields1 }, TypeEnum::TRecord { fields: fields2 }) => {
-                self.map_eq(fields1, fields2)
-            }
-            (
-                TypeEnum::TObj {
-                    obj_id: id1,
-                    params: params1,
-                    ..
-                },
-                TypeEnum::TObj {
-                    obj_id: id2,
-                    params: params2,
-                    ..
-                },
-            ) => id1 == id2 && self.map_eq(params1, params2),
-            // TCall and TFunc are not yet implemented
             _ => false,
         }
     }
-
-    fn map_eq<K>(&mut self, map1: &Mapping<K>, map2: &Mapping<K>) -> bool
-    where
-        K: std::hash::Hash + std::cmp::Eq + std::clone::Clone,
-    {
-        if map1.len() != map2.len() {
-            return false;
-        }
-        for (k, v) in map1.iter() {
-            if !map2.get(k).map(|v1| self.eq(*v, *v1)).unwrap_or(false) {
-                return false;
-            }
-        }
-        true
-    }
 }

nac3core/src/typecheck/typedef/test.rs

@@ -1,8 +1,69 @@
-use super::super::typedef::*;
+use super::*;
 use itertools::Itertools;
 use std::collections::HashMap;
 use test_case::test_case;
 
+impl Unifier {
+    /// Check whether two types are equal.
+    fn eq(&mut self, a: Type, b: Type) -> bool {
+        use TypeVarMeta::*;
+        if a == b {
+            return true;
+        }
+        let (ty_a, ty_b) = {
+            let table = &mut self.unification_table;
+            if table.unioned(a, b) {
+                return true;
+            }
+            (table.probe_value(a).clone(), table.probe_value(b).clone())
+        };
+
+        match (&*ty_a, &*ty_b) {
+            (
+                TypeEnum::TVar { meta: Generic, id: id1, .. },
+                TypeEnum::TVar { meta: Generic, id: id2, .. },
+            ) => id1 == id2,
+            (
+                TypeEnum::TVar { meta: Sequence(map1), .. },
+                TypeEnum::TVar { meta: Sequence(map2), .. },
+            ) => self.map_eq(&map1.borrow(), &map2.borrow()),
+            (TypeEnum::TTuple { ty: ty1 }, TypeEnum::TTuple { ty: ty2 }) => {
+                ty1.len() == ty2.len()
+                    && ty1.iter().zip(ty2.iter()).all(|(t1, t2)| self.eq(*t1, *t2))
+            }
+            (TypeEnum::TList { ty: ty1 }, TypeEnum::TList { ty: ty2 })
+            | (TypeEnum::TVirtual { ty: ty1 }, TypeEnum::TVirtual { ty: ty2 }) => {
+                self.eq(*ty1, *ty2)
+            }
+            (
+                TypeEnum::TVar { meta: Record(fields1), .. },
+                TypeEnum::TVar { meta: Record(fields2), .. },
+            ) => self.map_eq(&fields1.borrow(), &fields2.borrow()),
+            (
+                TypeEnum::TObj { obj_id: id1, params: params1, .. },
+                TypeEnum::TObj { obj_id: id2, params: params2, .. },
+            ) => id1 == id2 && self.map_eq(params1, params2),
+            // TCall and TFunc are not yet implemented
+            _ => false,
+        }
+    }
+
+    fn map_eq<K>(&mut self, map1: &Mapping<K>, map2: &Mapping<K>) -> bool
+    where
+        K: std::hash::Hash + std::cmp::Eq + std::clone::Clone,
+    {
+        if map1.len() != map2.len() {
+            return false;
+        }
+        for (k, v) in map1.iter() {
+            if !map2.get(k).map(|v1| self.eq(*v, *v1)).unwrap_or(false) {
+                return false;
+            }
+        }
+        true
+    }
+}
+
 struct TestEnvironment {
     pub unifier: Unifier,
     type_mapping: HashMap<String, Type>,
@@ -47,10 +108,7 @@ impl TestEnvironment {
             }),
         );
 
-        TestEnvironment {
+        TestEnvironment { unifier, type_mapping }
-            unifier,
-            type_mapping,
-        }
     }
 
     fn parse(&mut self, typ: &str, mapping: &Mapping<String>) -> Type {
@@ -65,9 +123,7 @@ impl TestEnvironment {
         mapping: &Mapping<String>,
     ) -> (Type, &'b str) {
         // for testing only, so we can just panic when the input is malformed
-        let end = typ
+        let end = typ.find(|c| ['[', ',', ']', '='].contains(&c)).unwrap_or_else(|| typ.len());
-            .find(|c| ['[', ',', ']', '='].contains(&c))
-            .unwrap_or_else(|| typ.len());
         match &typ[..end] {
             "Tuple" => {
                 let mut s = &typ[end..];
@@ -97,7 +153,7 @@ impl TestEnvironment {
                     fields.insert(key, result.0);
                     s = result.1;
                 }
-                (self.unifier.add_ty(TypeEnum::TRecord { fields }), &s[1..])
+                (self.unifier.add_record(fields), &s[1..])
             }
             x => {
                 let mut s = &typ[end..];
@@ -106,7 +162,7 @@ impl TestEnvironment {
                     // we should not resolve the type of type variables.
                     let mut ty = *self.type_mapping.get(x).unwrap();
                     let te = self.unifier.get_ty(ty);
-                    if let TypeEnum::TObj { params, .. } = &*te.as_ref().borrow() {
+                    if let TypeEnum::TObj { params, .. } = &*te.as_ref() {
                         if !params.is_empty() {
                             assert!(&s[0..1] == "[");
                             let mut p = Vec::new();
@@ -192,6 +248,7 @@ fn test_unify(
             env.unifier.unify(t1, t2).unwrap();
         }
         for (a, b) in verify_pairs.iter() {
+            println!("{} = {}", a, b);
             let t1 = env.parse(a, &mapping);
             let t2 = env.parse(b, &mapping);
             assert!(env.unifier.eq(t1, t2));
@@ -258,10 +315,8 @@ fn test_invalid_unification(
         let t2 = env.parse(b, &mapping);
         pairs.push((t1, t2));
     }
-    let (t1, t2) = (
+    let (t1, t2) =
-        env.parse(errornous_pair.0 .0, &mapping),
+        (env.parse(errornous_pair.0 .0, &mapping), env.parse(errornous_pair.0 .1, &mapping));
-        env.parse(errornous_pair.0 .1, &mapping),
-    );
     for (a, b) in pairs {
         env.unifier.unify(a, b).unwrap();
     }