diff --git a/nac3artiq/src/codegen.rs b/nac3artiq/src/codegen.rs
index 994c5048..914798c0 100644
--- a/nac3artiq/src/codegen.rs
+++ b/nac3artiq/src/codegen.rs
@@ -6,8 +6,8 @@ use nac3core::{
         CodeGenContext, CodeGenerator,
     },
     symbol_resolver::ValueEnum,
-    toplevel::{helper::PrimDef, DefinitionId, GenCall},
-    typecheck::typedef::{FunSignature, FuncArg, Type, TypeEnum, VarMap},
+    toplevel::{helper::PrimDef, numpy::unpack_ndarray_var_tys, DefinitionId, GenCall},
+    typecheck::typedef::{iter_type_vars, FunSignature, FuncArg, Type, TypeEnum, VarMap},
 };
 
 use nac3parser::ast::{Expr, ExprKind, Located, Stmt, StmtKind, StrRef};
@@ -23,7 +23,6 @@ use pyo3::{
 
 use crate::{symbol_resolver::InnerResolver, timeline::TimeFns};
 
-use nac3core::toplevel::numpy::unpack_ndarray_var_tys;
 use std::{
     collections::hash_map::DefaultHasher,
     collections::HashMap,
@@ -394,9 +393,11 @@ fn gen_rpc_tag(
                     gen_rpc_tag(ctx, *ty, buffer)?;
                 }
             }
-            TList { ty } => {
+            TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                let ty = iter_type_vars(params).next().unwrap().ty;
+
                 buffer.push(b'l');
-                gen_rpc_tag(ctx, *ty, buffer)?;
+                gen_rpc_tag(ctx, ty, buffer)?;
             }
             TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                 let (ndarray_dtype, ndarray_ndims) = unpack_ndarray_var_tys(&mut ctx.unifier, ty);
@@ -675,8 +676,10 @@ pub fn attributes_writeback(
                         host_attributes.append(pydict)?;
                     }
                 }
-                TypeEnum::TList { ty: elem_ty } => {
-                    if gen_rpc_tag(ctx, *elem_ty, &mut scratch_buffer).is_ok() {
+                TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                    let elem_ty = iter_type_vars(params).next().unwrap().ty;
+
+                    if gen_rpc_tag(ctx, elem_ty, &mut scratch_buffer).is_ok() {
                         let pydict = PyDict::new(py);
                         pydict.set_item("obj", val)?;
                         host_attributes.append(pydict)?;
diff --git a/nac3artiq/src/symbol_resolver.rs b/nac3artiq/src/symbol_resolver.rs
index 62597b8c..125e1bbf 100644
--- a/nac3artiq/src/symbol_resolver.rs
+++ b/nac3artiq/src/symbol_resolver.rs
@@ -329,8 +329,19 @@ impl InnerResolver {
             Ok(Ok((primitives.exception, true)))
         } else if ty_id == self.primitive_ids.list {
             // do not handle type var param and concrete check here
+            let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+                &*unifier.get_ty_immutable(primitives.list)
+            {
+                assert_eq!(*obj_id, PrimDef::List.id());
+                iter_type_vars(params).nth(0).unwrap()
+            } else {
+                unreachable!()
+            };
+
             let var = unifier.get_dummy_var().ty;
-            let list = unifier.add_ty(TypeEnum::TList { ty: var });
+            let list = unifier
+                .subst(primitives.list, &into_var_map([TypeVar { id: list_tvar.id, ty: var }]))
+                .unwrap();
             Ok(Ok((list, false)))
         } else if ty_id == self.primitive_ids.ndarray {
             // do not handle type var param and concrete check here
@@ -460,7 +471,7 @@ impl InnerResolver {
                 };
 
             match &*unifier.get_ty(origin_ty) {
-                TypeEnum::TList { .. } => {
+                TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::List.id() => {
                     if args.len() == 1 {
                         let ty = match self.get_pyty_obj_type(
                             py,
@@ -477,7 +488,21 @@ impl InnerResolver {
                                 "type list should take concrete parameters in typevar range".into(),
                             ));
                         }
-                        Ok(Ok((unifier.add_ty(TypeEnum::TList { ty: ty.0 }), true)))
+                        let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+                            &*unifier.get_ty_immutable(primitives.list)
+                        {
+                            assert_eq!(*obj_id, PrimDef::List.id());
+                            iter_type_vars(params).nth(0).unwrap()
+                        } else {
+                            unreachable!()
+                        };
+                        let list = unifier
+                            .subst(
+                                primitives.list,
+                                &into_var_map([TypeVar { id: list_tvar.id, ty: ty.0 }]),
+                            )
+                            .unwrap();
+                        Ok(Ok((list, true)))
                     } else {
                         return Ok(Err(format!(
                             "type list needs exactly 1 type parameters, found {}",
@@ -693,11 +718,12 @@ impl InnerResolver {
         };
         match (&*unifier.get_ty(extracted_ty), inst_check) {
             // do the instantiation for these four types
-            (TypeEnum::TList { ty }, false) => {
+            (TypeEnum::TObj { obj_id, params, .. }, false) if *obj_id == PrimDef::List.id() => {
+                let ty = iter_type_vars(params).nth(0).unwrap().ty;
                 let len: usize = self.helper.len_fn.call1(py, (obj,))?.extract(py)?;
                 if len == 0 {
                     assert!(matches!(
-                        &*unifier.get_ty(*ty),
+                        &*unifier.get_ty(ty),
                         TypeEnum::TVar { fields: None, range, .. }
                             if range.is_empty()
                     ));
@@ -706,8 +732,25 @@ impl InnerResolver {
                     let actual_ty =
                         self.get_list_elem_type(py, obj, len, unifier, defs, primitives)?;
                     match actual_ty {
-                        Ok(t) => match unifier.unify(*ty, t) {
-                            Ok(()) => Ok(Ok(unifier.add_ty(TypeEnum::TList { ty: *ty }))),
+                        Ok(t) => match unifier.unify(ty, t) {
+                            Ok(()) => {
+                                let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+                                    &*unifier.get_ty_immutable(primitives.list)
+                                {
+                                    assert_eq!(*obj_id, PrimDef::List.id());
+                                    iter_type_vars(params).nth(0).unwrap()
+                                } else {
+                                    unreachable!()
+                                };
+                                let list = unifier
+                                    .subst(
+                                        primitives.list,
+                                        &into_var_map([TypeVar { id: list_tvar.id, ty }]),
+                                    )
+                                    .unwrap();
+                                Ok(Ok(list))
+                            }
+
                             Err(e) => Ok(Err(format!(
                                 "type error ({}) for the list",
                                 e.to_display(unifier)
@@ -942,12 +985,11 @@ impl InnerResolver {
             }
 
             let len: usize = self.helper.len_fn.call1(py, (obj,))?.extract(py)?;
-            let elem_ty = if let TypeEnum::TList { ty } =
-                ctx.unifier.get_ty_immutable(expected_ty).as_ref()
-            {
-                *ty
-            } else {
-                unreachable!("must be list")
+            let elem_ty = match ctx.unifier.get_ty_immutable(expected_ty).as_ref() {
+                TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                    iter_type_vars(params).nth(0).unwrap().ty
+                }
+                _ => unreachable!("must be list"),
             };
             let ty = ctx.get_llvm_type(generator, elem_ty);
             let size_t = generator.get_size_type(ctx.ctx);
diff --git a/nac3core/src/codegen/concrete_type.rs b/nac3core/src/codegen/concrete_type.rs
index 15d063c5..6488ec61 100644
--- a/nac3core/src/codegen/concrete_type.rs
+++ b/nac3core/src/codegen/concrete_type.rs
@@ -47,9 +47,6 @@ pub enum ConcreteTypeEnum {
     TTuple {
         ty: Vec<ConcreteType>,
     },
-    TList {
-        ty: ConcreteType,
-    },
     TObj {
         obj_id: DefinitionId,
         fields: HashMap<StrRef, (ConcreteType, bool)>,
@@ -167,9 +164,6 @@ impl ConcreteTypeStore {
                         .map(|t| self.from_unifier_type(unifier, primitives, *t, cache))
                         .collect(),
                 },
-                TypeEnum::TList { ty } => ConcreteTypeEnum::TList {
-                    ty: self.from_unifier_type(unifier, primitives, *ty, cache),
-                },
                 TypeEnum::TObj { obj_id, fields, params } => ConcreteTypeEnum::TObj {
                     obj_id: *obj_id,
                     fields: fields
@@ -260,9 +254,6 @@ impl ConcreteTypeStore {
                     .map(|cty| self.to_unifier_type(unifier, primitives, *cty, cache))
                     .collect(),
             },
-            ConcreteTypeEnum::TList { ty } => {
-                TypeEnum::TList { ty: self.to_unifier_type(unifier, primitives, *ty, cache) }
-            }
             ConcreteTypeEnum::TVirtual { ty } => {
                 TypeEnum::TVirtual { ty: self.to_unifier_type(unifier, primitives, *ty, cache) }
             }
diff --git a/nac3core/src/codegen/expr.rs b/nac3core/src/codegen/expr.rs
index 2d188058..be8e6b4f 100644
--- a/nac3core/src/codegen/expr.rs
+++ b/nac3core/src/codegen/expr.rs
@@ -2124,11 +2124,19 @@ pub fn gen_expr<'ctx, G: CodeGenerator>(
             }
 
             let ty = if elements.is_empty() {
-                let TypeEnum::TList { ty } = &*ctx.unifier.get_ty(expr.custom.unwrap()) else {
+                let ty = if let TypeEnum::TObj { obj_id, params, .. } =
+                    &*ctx.unifier.get_ty(expr.custom.unwrap())
+                {
+                    if *obj_id != PrimDef::List.id() {
+                        unreachable!()
+                    }
+
+                    *params.iter().next().unwrap().1
+                } else {
                     unreachable!()
                 };
 
-                ctx.get_llvm_type(generator, *ty)
+                ctx.get_llvm_type(generator, ty)
             } else {
                 elements[0].get_type()
             };
@@ -2550,7 +2558,9 @@ pub fn gen_expr<'ctx, G: CodeGenerator>(
         }
         ExprKind::Subscript { value, slice, .. } => {
             match &*ctx.unifier.get_ty(value.custom.unwrap()) {
-                TypeEnum::TList { ty } => {
+                TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                    let ty = params.iter().next().unwrap().1;
+
                     let v = if let Some(v) = generator.gen_expr(ctx, value)? {
                         v.to_basic_value_enum(ctx, generator, value.custom.unwrap())?
                             .into_pointer_value()
diff --git a/nac3core/src/codegen/mod.rs b/nac3core/src/codegen/mod.rs
index eb3b9d95..17952369 100644
--- a/nac3core/src/codegen/mod.rs
+++ b/nac3core/src/codegen/mod.rs
@@ -456,6 +456,20 @@ fn get_llvm_type<'ctx, G: CodeGenerator + ?Sized>(
                             .into()
                         }
 
+                        TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                            let element_type = get_llvm_type(
+                                ctx,
+                                module,
+                                generator,
+                                unifier,
+                                top_level,
+                                type_cache,
+                                *params.iter().next().unwrap().1,
+                            );
+
+                            ListType::new(generator, ctx, element_type).as_base_type().into()
+                        }
+
                         TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                             let (dtype, _) = unpack_ndarray_var_tys(unifier, ty);
                             let element_type = get_llvm_type(
@@ -516,12 +530,6 @@ fn get_llvm_type<'ctx, G: CodeGenerator + ?Sized>(
                     .collect_vec();
                 ctx.struct_type(&fields, false).into()
             }
-            TList { ty } => {
-                let element_type =
-                    get_llvm_type(ctx, module, generator, unifier, top_level, type_cache, *ty);
-
-                ListType::new(generator, ctx, element_type).as_base_type().into()
-            }
             TVirtual { .. } => unimplemented!(),
             _ => unreachable!("{}", ty_enum.get_type_name()),
         };
diff --git a/nac3core/src/codegen/numpy.rs b/nac3core/src/codegen/numpy.rs
index 3811ac0b..4db8a81f 100644
--- a/nac3core/src/codegen/numpy.rs
+++ b/nac3core/src/codegen/numpy.rs
@@ -1804,10 +1804,15 @@ pub fn gen_ndarray_array<'ctx>(
             unpack_ndarray_var_tys(&mut context.unifier, obj_ty).0
         }
 
-        TypeEnum::TList { ty } => {
-            let mut ty = *ty;
-            while let TypeEnum::TList { ty: elem_ty } = &*context.unifier.get_ty_immutable(ty) {
-                ty = *elem_ty;
+        TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+            let mut ty = *params.iter().next().unwrap().1;
+            while let TypeEnum::TObj { obj_id, params, .. } = &*context.unifier.get_ty_immutable(ty)
+            {
+                if *obj_id != PrimDef::List.id() {
+                    break;
+                }
+
+                ty = *params.iter().next().unwrap().1;
             }
             ty
         }
diff --git a/nac3core/src/codegen/stmt.rs b/nac3core/src/codegen/stmt.rs
index 5bae9a94..94266ca2 100644
--- a/nac3core/src/codegen/stmt.rs
+++ b/nac3core/src/codegen/stmt.rs
@@ -136,7 +136,7 @@ pub fn gen_store_target<'ctx, G: CodeGenerator>(
         }
         ExprKind::Subscript { value, slice, .. } => {
             match ctx.unifier.get_ty_immutable(value.custom.unwrap()).as_ref() {
-                TypeEnum::TList { .. } => {
+                TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::List.id() => {
                     let v = generator
                         .gen_expr(ctx, value)?
                         .unwrap()
@@ -243,7 +243,9 @@ pub fn gen_assign<'ctx, G: CodeGenerator>(
                 .into_pointer_value();
             let value = ListValue::from_ptr_val(value, llvm_usize, None);
             let ty = match &*ctx.unifier.get_ty_immutable(target.custom.unwrap()) {
-                TypeEnum::TList { ty } => *ty,
+                TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                    *params.iter().next().unwrap().1
+                }
                 TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                     unpack_ndarray_var_tys(&mut ctx.unifier, target.custom.unwrap()).0
                 }
diff --git a/nac3core/src/symbol_resolver.rs b/nac3core/src/symbol_resolver.rs
index 753cc076..ce9c0985 100644
--- a/nac3core/src/symbol_resolver.rs
+++ b/nac3core/src/symbol_resolver.rs
@@ -382,13 +382,12 @@ pub trait SymbolResolver {
 }
 
 thread_local! {
-    static IDENTIFIER_ID: [StrRef; 12] = [
+    static IDENTIFIER_ID: [StrRef; 11] = [
         "int32".into(),
         "int64".into(),
         "float".into(),
         "bool".into(),
         "virtual".into(),
-        "list".into(),
         "tuple".into(),
         "str".into(),
         "Exception".into(),
@@ -413,13 +412,12 @@ pub fn parse_type_annotation<T>(
     let float_id = ids[2];
     let bool_id = ids[3];
     let virtual_id = ids[4];
-    let list_id = ids[5];
-    let tuple_id = ids[6];
-    let str_id = ids[7];
-    let exn_id = ids[8];
-    let uint32_id = ids[9];
-    let uint64_id = ids[10];
-    let literal_id = ids[11];
+    let tuple_id = ids[5];
+    let str_id = ids[6];
+    let exn_id = ids[7];
+    let uint32_id = ids[8];
+    let uint64_id = ids[9];
+    let literal_id = ids[10];
 
     let name_handling = |id: &StrRef, loc: Location, unifier: &mut Unifier| {
         if *id == int32_id {
@@ -476,9 +474,6 @@ pub fn parse_type_annotation<T>(
         if *id == virtual_id {
             let ty = parse_type_annotation(resolver, top_level_defs, unifier, primitives, slice)?;
             Ok(unifier.add_ty(TypeEnum::TVirtual { ty }))
-        } else if *id == list_id {
-            let ty = parse_type_annotation(resolver, top_level_defs, unifier, primitives, slice)?;
-            Ok(unifier.add_ty(TypeEnum::TList { ty }))
         } else if *id == tuple_id {
             if let Tuple { elts, .. } = &slice.node {
                 let ty = elts
diff --git a/nac3core/src/toplevel/builtins.rs b/nac3core/src/toplevel/builtins.rs
index 2524b9a7..954367c8 100644
--- a/nac3core/src/toplevel/builtins.rs
+++ b/nac3core/src/toplevel/builtins.rs
@@ -305,6 +305,8 @@ struct BuiltinBuilder<'a> {
     unwrap_ty: (Type, bool),
     option_tvar: TypeVar,
 
+    list_tvar: TypeVar,
+
     ndarray_dtype_tvar: TypeVar,
     ndarray_ndims_tvar: TypeVar,
     ndarray_copy_ty: (Type, bool),
@@ -395,7 +397,17 @@ impl<'a> BuiltinBuilder<'a> {
             unifier.get_fresh_var_with_range(&[num_ty.ty, ndarray_num_ty], Some("T".into()), None);
         let num_or_ndarray_var_map = into_var_map([num_ty, num_or_ndarray_ty]);
 
-        let list_int32 = unifier.add_ty(TypeEnum::TList { ty: int32 });
+        let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+            &*unifier.get_ty_immutable(primitives.list)
+        {
+            assert_eq!(*obj_id, PrimDef::List.id());
+            iter_type_vars(params).nth(0).unwrap()
+        } else {
+            unreachable!()
+        };
+        let list_int32 = unifier
+            .subst(primitives.list, &into_var_map([TypeVar { id: list_tvar.id, ty: int32 }]))
+            .unwrap();
 
         let ndarray_factory_fn_shape_arg_tvar = unifier.get_fresh_var(Some("Shape".into()), None);
 
@@ -407,6 +419,8 @@ impl<'a> BuiltinBuilder<'a> {
             unwrap_ty,
             option_tvar,
 
+            list_tvar,
+
             ndarray_dtype_tvar,
             ndarray_ndims_tvar,
             ndarray_copy_ty,
@@ -457,6 +471,8 @@ impl<'a> BuiltinBuilder<'a> {
             | PrimDef::OptionUnwrap
             | PrimDef::FunSome => self.build_option_class_related(prim),
 
+            PrimDef::List => self.build_list_class_related(prim),
+
             PrimDef::NDArray | PrimDef::NDArrayCopy | PrimDef::NDArrayFill => {
                 self.build_ndarray_class_related(prim)
             }
@@ -735,6 +751,27 @@ impl<'a> BuiltinBuilder<'a> {
         }
     }
 
+    fn build_list_class_related(&self, prim: PrimDef) -> TopLevelDef {
+        debug_assert_prim_is_allowed(prim, &[PrimDef::List]);
+
+        match prim {
+            PrimDef::List => TopLevelDef::Class {
+                name: prim.name().into(),
+                object_id: prim.id(),
+                type_vars: vec![self.list_tvar.ty],
+                fields: Vec::default(),
+                attributes: Vec::default(),
+                methods: Vec::default(),
+                ancestors: Vec::default(),
+                constructor: None,
+                resolver: None,
+                loc: None,
+            },
+
+            _ => unreachable!(),
+        }
+    }
+
     /// Build the class `ndarray` and its associated methods.
     fn build_ndarray_class_related(&self, prim: PrimDef) -> TopLevelDef {
         debug_assert_prim_is_allowed(
@@ -1335,7 +1372,13 @@ impl<'a> BuiltinBuilder<'a> {
         let PrimitiveStore { uint64, int32, .. } = *self.primitives;
 
         let tvar = self.unifier.get_fresh_var(Some("L".into()), None);
-        let list = self.unifier.add_ty(TypeEnum::TList { ty: tvar.ty });
+        let list = self
+            .unifier
+            .subst(
+                self.primitives.list,
+                &into_var_map([TypeVar { id: self.list_tvar.id, ty: tvar.ty }]),
+            )
+            .unwrap();
         let ndims = self.unifier.get_fresh_const_generic_var(uint64, Some("N".into()), None);
         let ndarray = make_ndarray_ty(self.unifier, self.primitives, Some(tvar.ty), Some(ndims.ty));
 
@@ -1367,7 +1410,7 @@ impl<'a> BuiltinBuilder<'a> {
                         Some(calculate_len_for_slice_range(generator, ctx, start, end, step).into())
                     } else {
                         match &*ctx.unifier.get_ty_immutable(arg_ty) {
-                            TypeEnum::TList { .. } => {
+                            TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::List.id() => {
                                 let int32 = ctx.ctx.i32_type();
                                 let zero = int32.const_zero();
                                 let len = ctx
diff --git a/nac3core/src/toplevel/helper.rs b/nac3core/src/toplevel/helper.rs
index 73812505..9fef74eb 100644
--- a/nac3core/src/toplevel/helper.rs
+++ b/nac3core/src/toplevel/helper.rs
@@ -2,7 +2,7 @@ use std::convert::TryInto;
 
 use crate::symbol_resolver::SymbolValue;
 use crate::toplevel::numpy::unpack_ndarray_var_tys;
-use crate::typecheck::typedef::{into_var_map, Mapping, TypeVarId, VarMap};
+use crate::typecheck::typedef::{into_var_map, iter_type_vars, Mapping, TypeVarId, VarMap};
 use nac3parser::ast::{Constant, Location};
 use strum::IntoEnumIterator;
 use strum_macros::EnumIter;
@@ -12,6 +12,7 @@ use super::*;
 /// All primitive types and functions in nac3core.
 #[derive(Clone, Copy, Debug, EnumIter, PartialEq, Eq)]
 pub enum PrimDef {
+    // Classes
     Int32,
     Int64,
     Float,
@@ -23,10 +24,13 @@ pub enum PrimDef {
     UInt32,
     UInt64,
     Option,
+    List,
+    NDArray,
+
+    // Member Functions
     OptionIsSome,
     OptionIsNone,
     OptionUnwrap,
-    NDArray,
     NDArrayCopy,
     NDArrayFill,
     FunInt32,
@@ -99,6 +103,8 @@ pub enum PrimDef {
     FunNpLdExp,
     FunNpHypot,
     FunNpNextAfter,
+
+    // Top-Level Functions
     FunSome,
 }
 
@@ -177,6 +183,7 @@ impl PrimDef {
             PrimDef::OptionIsSome => fun("Option.is_some", Some("is_some")),
             PrimDef::OptionIsNone => fun("Option.is_none", Some("is_none")),
             PrimDef::OptionUnwrap => fun("Option.unwrap", Some("unwrap")),
+            PrimDef::List => class("list"),
             PrimDef::NDArray => class("ndarray"),
             PrimDef::NDArrayCopy => fun("ndarray.copy", Some("copy")),
             PrimDef::NDArrayFill => fun("ndarray.fill", Some("fill")),
@@ -410,6 +417,13 @@ impl TopLevelComposer {
             _ => unreachable!(),
         };
 
+        let list_elem_tvar = unifier.get_fresh_var(Some("list_elem".into()), None);
+        let list = unifier.add_ty(TypeEnum::TObj {
+            obj_id: PrimDef::List.id(),
+            fields: Mapping::new(),
+            params: into_var_map([list_elem_tvar]),
+        });
+
         let ndarray_dtype_tvar = unifier.get_fresh_var(Some("ndarray_dtype".into()), None);
         let ndarray_ndims_tvar =
             unifier.get_fresh_const_generic_var(size_t_ty, Some("ndarray_ndims".into()), None);
@@ -451,6 +465,7 @@ impl TopLevelComposer {
             str,
             exception,
             option,
+            list,
             ndarray,
             size_t,
         };
@@ -888,7 +903,9 @@ pub fn arraylike_flatten_element_type(unifier: &mut Unifier, ty: Type) -> Type {
             unpack_ndarray_var_tys(unifier, ty).0
         }
 
-        TypeEnum::TList { ty } => arraylike_flatten_element_type(unifier, *ty),
+        TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+            arraylike_flatten_element_type(unifier, iter_type_vars(params).next().unwrap().ty)
+        }
         _ => ty,
     }
 }
@@ -909,7 +926,9 @@ pub fn arraylike_get_ndims(unifier: &mut Unifier, ty: Type) -> u64 {
             u64::try_from(values[0].clone()).unwrap()
         }
 
-        TypeEnum::TList { ty } => arraylike_get_ndims(unifier, *ty) + 1,
+        TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+            arraylike_get_ndims(unifier, iter_type_vars(params).next().unwrap().ty) + 1
+        }
         _ => 0,
     }
 }
diff --git a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__generic_class.snap b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__generic_class.snap
index 82ab00e4..ed94a833 100644
--- a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__generic_class.snap
+++ b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__generic_class.snap
@@ -5,7 +5,7 @@ expression: res_vec
 [
     "Class {\nname: \"Generic_A\",\nancestors: [\"Generic_A[V]\", \"B\"],\nfields: [\"aa\", \"a\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"foo\", \"fn[[b:T], none]\"), (\"fun\", \"fn[[a:int32], V]\")],\ntype_vars: [\"V\"]\n}\n",
     "Function {\nname: \"Generic_A.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
-    "Function {\nname: \"Generic_A.fun\",\nsig: \"fn[[a:int32], V]\",\nvar_id: [TypeVarId(240)]\n}\n",
+    "Function {\nname: \"Generic_A.fun\",\nsig: \"fn[[a:int32], V]\",\nvar_id: [TypeVarId(242)]\n}\n",
     "Class {\nname: \"B\",\nancestors: [\"B\"],\nfields: [\"aa\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"foo\", \"fn[[b:T], none]\")],\ntype_vars: []\n}\n",
     "Function {\nname: \"B.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"B.foo\",\nsig: \"fn[[b:T], none]\",\nvar_id: []\n}\n",
diff --git a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__inheritance_override.snap b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__inheritance_override.snap
index d3301d00..2c59687c 100644
--- a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__inheritance_override.snap
+++ b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__inheritance_override.snap
@@ -7,7 +7,7 @@ expression: res_vec
     "Function {\nname: \"A.__init__\",\nsig: \"fn[[t:T], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"A.fun\",\nsig: \"fn[[a:int32, b:T], list[virtual[B[bool]]]]\",\nvar_id: []\n}\n",
     "Function {\nname: \"A.foo\",\nsig: \"fn[[c:C], none]\",\nvar_id: []\n}\n",
-    "Class {\nname: \"B\",\nancestors: [\"B[typevar229]\", \"A[float]\"],\nfields: [\"a\", \"b\", \"c\", \"d\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[a:int32, b:T], list[virtual[B[bool]]]]\"), (\"foo\", \"fn[[c:C], none]\")],\ntype_vars: [\"typevar229\"]\n}\n",
+    "Class {\nname: \"B\",\nancestors: [\"B[typevar231]\", \"A[float]\"],\nfields: [\"a\", \"b\", \"c\", \"d\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[a:int32, b:T], list[virtual[B[bool]]]]\"), (\"foo\", \"fn[[c:C], none]\")],\ntype_vars: [\"typevar231\"]\n}\n",
     "Function {\nname: \"B.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"B.fun\",\nsig: \"fn[[a:int32, b:T], list[virtual[B[bool]]]]\",\nvar_id: []\n}\n",
     "Class {\nname: \"C\",\nancestors: [\"C\", \"B[bool]\", \"A[float]\"],\nfields: [\"a\", \"b\", \"c\", \"d\", \"e\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[a:int32, b:T], list[virtual[B[bool]]]]\"), (\"foo\", \"fn[[c:C], none]\")],\ntype_vars: []\n}\n",
diff --git a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__list_tuple_generic.snap b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__list_tuple_generic.snap
index 911426b9..2aa2ead6 100644
--- a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__list_tuple_generic.snap
+++ b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__list_tuple_generic.snap
@@ -5,8 +5,8 @@ expression: res_vec
 [
     "Function {\nname: \"foo\",\nsig: \"fn[[a:list[int32], b:tuple[T, float]], A[B, bool]]\",\nvar_id: []\n}\n",
     "Class {\nname: \"A\",\nancestors: [\"A[T, V]\"],\nfields: [\"a\", \"b\"],\nmethods: [(\"__init__\", \"fn[[v:V], none]\"), (\"fun\", \"fn[[a:T], V]\")],\ntype_vars: [\"T\", \"V\"]\n}\n",
-    "Function {\nname: \"A.__init__\",\nsig: \"fn[[v:V], none]\",\nvar_id: [TypeVarId(242)]\n}\n",
-    "Function {\nname: \"A.fun\",\nsig: \"fn[[a:T], V]\",\nvar_id: [TypeVarId(247)]\n}\n",
+    "Function {\nname: \"A.__init__\",\nsig: \"fn[[v:V], none]\",\nvar_id: [TypeVarId(244)]\n}\n",
+    "Function {\nname: \"A.fun\",\nsig: \"fn[[a:T], V]\",\nvar_id: [TypeVarId(249)]\n}\n",
     "Function {\nname: \"gfun\",\nsig: \"fn[[a:A[list[float], int32]], none]\",\nvar_id: []\n}\n",
     "Class {\nname: \"B\",\nancestors: [\"B\"],\nfields: [],\nmethods: [(\"__init__\", \"fn[[], none]\")],\ntype_vars: []\n}\n",
     "Function {\nname: \"B.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
diff --git a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__self1.snap b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__self1.snap
index d60daf83..a350d18a 100644
--- a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__self1.snap
+++ b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__self1.snap
@@ -3,7 +3,7 @@ source: nac3core/src/toplevel/test.rs
 expression: res_vec
 ---
 [
-    "Class {\nname: \"A\",\nancestors: [\"A[typevar228, typevar229]\"],\nfields: [\"a\", \"b\"],\nmethods: [(\"__init__\", \"fn[[a:A[float, bool], b:B], none]\"), (\"fun\", \"fn[[a:A[float, bool]], A[bool, int32]]\")],\ntype_vars: [\"typevar228\", \"typevar229\"]\n}\n",
+    "Class {\nname: \"A\",\nancestors: [\"A[typevar230, typevar231]\"],\nfields: [\"a\", \"b\"],\nmethods: [(\"__init__\", \"fn[[a:A[float, bool], b:B], none]\"), (\"fun\", \"fn[[a:A[float, bool]], A[bool, int32]]\")],\ntype_vars: [\"typevar230\", \"typevar231\"]\n}\n",
     "Function {\nname: \"A.__init__\",\nsig: \"fn[[a:A[float, bool], b:B], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"A.fun\",\nsig: \"fn[[a:A[float, bool]], A[bool, int32]]\",\nvar_id: []\n}\n",
     "Class {\nname: \"B\",\nancestors: [\"B\", \"A[int64, bool]\"],\nfields: [\"a\", \"b\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[a:A[float, bool]], A[bool, int32]]\"), (\"foo\", \"fn[[b:B], B]\"), (\"bar\", \"fn[[a:A[list[B], int32]], tuple[A[virtual[A[B, int32]], bool], B]]\")],\ntype_vars: []\n}\n",
diff --git a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__simple_class_compose.snap b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__simple_class_compose.snap
index 0fea9e25..5fe92b13 100644
--- a/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__simple_class_compose.snap
+++ b/nac3core/src/toplevel/snapshots/nac3core__toplevel__test__test_analyze__simple_class_compose.snap
@@ -6,12 +6,12 @@ expression: res_vec
     "Class {\nname: \"A\",\nancestors: [\"A\"],\nfields: [\"a\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[b:B], none]\"), (\"foo\", \"fn[[a:T, b:V], none]\")],\ntype_vars: []\n}\n",
     "Function {\nname: \"A.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"A.fun\",\nsig: \"fn[[b:B], none]\",\nvar_id: []\n}\n",
-    "Function {\nname: \"A.foo\",\nsig: \"fn[[a:T, b:V], none]\",\nvar_id: [TypeVarId(248)]\n}\n",
+    "Function {\nname: \"A.foo\",\nsig: \"fn[[a:T, b:V], none]\",\nvar_id: [TypeVarId(250)]\n}\n",
     "Class {\nname: \"B\",\nancestors: [\"B\", \"C\", \"A\"],\nfields: [\"a\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[b:B], none]\"), (\"foo\", \"fn[[a:T, b:V], none]\")],\ntype_vars: []\n}\n",
     "Function {\nname: \"B.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
     "Class {\nname: \"C\",\nancestors: [\"C\", \"A\"],\nfields: [\"a\"],\nmethods: [(\"__init__\", \"fn[[], none]\"), (\"fun\", \"fn[[b:B], none]\"), (\"foo\", \"fn[[a:T, b:V], none]\")],\ntype_vars: []\n}\n",
     "Function {\nname: \"C.__init__\",\nsig: \"fn[[], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"C.fun\",\nsig: \"fn[[b:B], none]\",\nvar_id: []\n}\n",
     "Function {\nname: \"foo\",\nsig: \"fn[[a:A], none]\",\nvar_id: []\n}\n",
-    "Function {\nname: \"ff\",\nsig: \"fn[[a:T], V]\",\nvar_id: [TypeVarId(256)]\n}\n",
+    "Function {\nname: \"ff\",\nsig: \"fn[[a:T], V]\",\nvar_id: [TypeVarId(258)]\n}\n",
 ]
diff --git a/nac3core/src/toplevel/test.rs b/nac3core/src/toplevel/test.rs
index 4651ab21..7678452d 100644
--- a/nac3core/src/toplevel/test.rs
+++ b/nac3core/src/toplevel/test.rs
@@ -1,3 +1,6 @@
+use super::*;
+use crate::toplevel::helper::PrimDef;
+use crate::typecheck::typedef::into_var_map;
 use crate::{
     codegen::CodeGenContext,
     symbol_resolver::{SymbolResolver, ValueEnum},
@@ -14,8 +17,6 @@ use parking_lot::Mutex;
 use std::{collections::HashMap, sync::Arc};
 use test_case::test_case;
 
-use super::*;
-
 struct ResolverInternal {
     id_to_type: Mutex<HashMap<StrRef, Type>>,
     id_to_def: Mutex<HashMap<StrRef, DefinitionId>>,
@@ -775,8 +776,15 @@ fn make_internal_resolver_with_tvar(
     unifier: &mut Unifier,
     print: bool,
 ) -> Arc<ResolverInternal> {
+    let list_elem_tvar = unifier.get_fresh_var(Some("list_elem".into()), None);
+    let list = unifier.add_ty(TypeEnum::TObj {
+        obj_id: PrimDef::List.id(),
+        fields: HashMap::new(),
+        params: into_var_map([list_elem_tvar]),
+    });
+
     let res: Arc<ResolverInternal> = ResolverInternal {
-        id_to_def: Mutex::default(),
+        id_to_def: Mutex::new(HashMap::from([("list".into(), PrimDef::List.id())])),
         id_to_type: tvars
             .into_iter()
             .map(|(name, range)| {
@@ -790,7 +798,7 @@ fn make_internal_resolver_with_tvar(
             })
             .collect::<HashMap<_, _>>()
             .into(),
-        class_names: Mutex::default(),
+        class_names: Mutex::new(HashMap::from([("list".into(), list)])),
     }
     .into();
     if print {
diff --git a/nac3core/src/toplevel/type_annotation.rs b/nac3core/src/toplevel/type_annotation.rs
index f598badf..95d5acad 100644
--- a/nac3core/src/toplevel/type_annotation.rs
+++ b/nac3core/src/toplevel/type_annotation.rs
@@ -18,7 +18,6 @@ pub enum TypeAnnotation {
     TypeVar(Type),
     /// A `Literal` allowing a subset of literals.
     Literal(Vec<Constant>),
-    List(Box<TypeAnnotation>),
     Tuple(Vec<TypeAnnotation>),
 }
 
@@ -51,7 +50,6 @@ impl TypeAnnotation {
                 format!("Literal({})", values.iter().map(|v| format!("{v:?}")).join(", "))
             }
             Virtual(ty) => format!("virtual[{}]", ty.stringify(unifier)),
-            List(ty) => format!("list[{}]", ty.stringify(unifier)),
             Tuple(types) => {
                 format!(
                     "tuple[{}]",
@@ -145,9 +143,7 @@ pub fn parse_ast_to_type_annotation_kinds<T, S: std::hash::BuildHasher + Clone>(
          slice: &ast::Expr<T>,
          unifier: &mut Unifier,
          mut locked: HashMap<DefinitionId, Vec<Type>, S>| {
-            if ["virtual".into(), "Generic".into(), "list".into(), "tuple".into(), "Option".into()]
-                .contains(id)
-            {
+            if ["virtual".into(), "Generic".into(), "tuple".into(), "Option".into()].contains(id) {
                 return Err(HashSet::from([format!(
                     "keywords cannot be class name (at {})",
                     expr.location
@@ -236,23 +232,6 @@ pub fn parse_ast_to_type_annotation_kinds<T, S: std::hash::BuildHasher + Clone>(
             Ok(TypeAnnotation::Virtual(def.into()))
         }
 
-        // list
-        ast::ExprKind::Subscript { value, slice, .. }
-            if {
-                matches!(&value.node, ast::ExprKind::Name { id, .. } if id == &"list".into())
-            } =>
-        {
-            let def_ann = parse_ast_to_type_annotation_kinds(
-                resolver,
-                top_level_defs,
-                unifier,
-                primitives,
-                slice.as_ref(),
-                locked,
-            )?;
-            Ok(TypeAnnotation::List(def_ann.into()))
-        }
-
         // option
         ast::ExprKind::Subscript { value, slice, .. }
             if {
@@ -516,15 +495,6 @@ pub fn get_type_from_type_annotation_kinds(
             )?;
             Ok(unifier.add_ty(TypeEnum::TVirtual { ty }))
         }
-        TypeAnnotation::List(ty) => {
-            let ty = get_type_from_type_annotation_kinds(
-                top_level_defs,
-                unifier,
-                ty.as_ref(),
-                subst_list,
-            )?;
-            Ok(unifier.add_ty(TypeEnum::TList { ty }))
-        }
         TypeAnnotation::Tuple(tys) => {
             let tys = tys
                 .iter()
@@ -565,7 +535,7 @@ pub fn get_type_var_contained_in_type_annotation(ann: &TypeAnnotation) -> Vec<Ty
     let mut result: Vec<TypeAnnotation> = Vec::new();
     match ann {
         TypeAnnotation::TypeVar(..) => result.push(ann.clone()),
-        TypeAnnotation::Virtual(ann) | TypeAnnotation::List(ann) => {
+        TypeAnnotation::Virtual(ann) => {
             result.extend(get_type_var_contained_in_type_annotation(ann.as_ref()));
         }
         TypeAnnotation::CustomClass { params, .. } => {
@@ -606,8 +576,7 @@ pub fn check_overload_type_annotation_compatible(
 
             a == b
         }
-        (TypeAnnotation::Virtual(a), TypeAnnotation::Virtual(b))
-        | (TypeAnnotation::List(a), TypeAnnotation::List(b)) => {
+        (TypeAnnotation::Virtual(a), TypeAnnotation::Virtual(b)) => {
             check_overload_type_annotation_compatible(a.as_ref(), b.as_ref(), unifier)
         }
 
diff --git a/nac3core/src/typecheck/type_inferencer/mod.rs b/nac3core/src/typecheck/type_inferencer/mod.rs
index f879650f..c20fe78d 100644
--- a/nac3core/src/typecheck/type_inferencer/mod.rs
+++ b/nac3core/src/typecheck/type_inferencer/mod.rs
@@ -4,15 +4,20 @@ use std::iter::once;
 use std::ops::Not;
 use std::{cell::RefCell, sync::Arc};
 
-use super::typedef::{Call, FunSignature, FuncArg, RecordField, Type, TypeEnum, Unifier, VarMap};
-use super::{magic_methods::*, type_error::TypeError, typedef::CallId};
-use crate::toplevel::TopLevelDef;
+use super::{
+    magic_methods::*,
+    type_error::TypeError,
+    typedef::{
+        into_var_map, iter_type_vars, Call, CallId, FunSignature, FuncArg, RecordField, Type,
+        TypeEnum, TypeVar, Unifier, VarMap,
+    },
+};
 use crate::{
     symbol_resolver::{SymbolResolver, SymbolValue},
     toplevel::{
         helper::{arraylike_flatten_element_type, arraylike_get_ndims, PrimDef},
         numpy::{make_ndarray_ty, unpack_ndarray_var_tys},
-        TopLevelContext,
+        TopLevelContext, TopLevelDef,
     },
 };
 use itertools::{izip, Itertools};
@@ -50,6 +55,7 @@ pub struct PrimitiveStore {
     pub str: Type,
     pub exception: Type,
     pub option: Type,
+    pub list: Type,
     pub ndarray: Type,
     pub size_t: u32,
 }
@@ -242,8 +248,17 @@ impl<'a> Fold<()> for Inferencer<'a> {
                     self.unify(self.primitives.int32, target.custom.unwrap(), &target.location)?;
                 } else {
                     let list_like_ty = match &*self.unifier.get_ty(iter.custom.unwrap()) {
-                        TypeEnum::TList { .. } => {
-                            self.unifier.add_ty(TypeEnum::TList { ty: target.custom.unwrap() })
+                        TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                            let list_tvar = iter_type_vars(params).nth(0).unwrap();
+                            self.unifier
+                                .subst(
+                                    self.primitives.list,
+                                    &into_var_map([TypeVar {
+                                        id: list_tvar.id,
+                                        ty: target.custom.unwrap(),
+                                    }]),
+                                )
+                                .unwrap()
                         }
                         TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                             todo!()
@@ -764,6 +779,16 @@ impl<'a> Inferencer<'a> {
                 generators[0].target.location,
             );
         }
+
+        let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+            &*self.unifier.get_ty_immutable(self.primitives.list)
+        {
+            assert_eq!(*obj_id, PrimDef::List.id());
+            iter_type_vars(params).nth(0).unwrap()
+        } else {
+            unreachable!()
+        };
+
         let variable_mapping = self.variable_mapping.clone();
         let defined_identifiers = self.defined_identifiers.clone();
         let mut new_context = Inferencer {
@@ -792,7 +817,13 @@ impl<'a> Inferencer<'a> {
                 &target.location,
             )?;
         } else {
-            let list = new_context.unifier.add_ty(TypeEnum::TList { ty: target.custom.unwrap() });
+            let list = new_context
+                .unifier
+                .subst(
+                    self.primitives.list,
+                    &into_var_map([TypeVar { id: list_tvar.id, ty: target.custom.unwrap() }]),
+                )
+                .unwrap();
             new_context.unify(iter.custom.unwrap(), list, &iter.location)?;
         }
         let ifs: Vec<_> = generator
@@ -809,9 +840,16 @@ impl<'a> Inferencer<'a> {
             new_context.unify(v.custom.unwrap(), new_context.primitives.bool, &v.location)?;
         }
 
+        let custom = new_context
+            .unifier
+            .subst(
+                self.primitives.list,
+                &into_var_map([TypeVar { id: list_tvar.id, ty: elt.custom.unwrap() }]),
+            )
+            .unwrap();
         Ok(Located {
             location,
-            custom: Some(new_context.unifier.add_ty(TypeEnum::TList { ty: elt.custom.unwrap() })),
+            custom: Some(custom),
             node: ExprKind::ListComp {
                 elt: Box::new(elt),
                 generators: vec![Comprehension {
@@ -893,11 +931,13 @@ impl<'a> Inferencer<'a> {
         // Here, we also take the opportunity to deduce `ndims` statically.
         let shape_ty_enum = &*self.unifier.get_ty(shape_ty);
         let ndims = match shape_ty_enum {
-            TypeEnum::TList { ty } => {
+            TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
                 // Handle 1. A list of int32s
 
+                let ty = iter_type_vars(params).nth(0).unwrap().ty;
+
                 // Typecheck
-                self.unifier.unify(*ty, self.primitives.int32).map_err(|err| {
+                self.unifier.unify(ty, self.primitives.int32).map_err(|err| {
                     HashSet::from([err
                         .at(Some(shape.location))
                         .to_display(self.unifier)
@@ -1563,7 +1603,19 @@ impl<'a> Inferencer<'a> {
         for t in elts {
             self.unify(ty, t.custom.unwrap(), &t.location)?;
         }
-        Ok(self.unifier.add_ty(TypeEnum::TList { ty }))
+        let list_tvar = if let TypeEnum::TObj { obj_id, params, .. } =
+            &*self.unifier.get_ty_immutable(self.primitives.list)
+        {
+            assert_eq!(*obj_id, PrimDef::List.id());
+            iter_type_vars(params).nth(0).unwrap()
+        } else {
+            unreachable!()
+        };
+        let list = self
+            .unifier
+            .subst(self.primitives.list, &into_var_map([TypeVar { id: list_tvar.id, ty }]))
+            .unwrap();
+        Ok(list)
     }
 
     #[allow(clippy::unnecessary_wraps)]
@@ -1885,7 +1937,16 @@ impl<'a> Inferencer<'a> {
                     self.constrain(v.custom.unwrap(), self.primitives.int32, &v.location)?;
                 }
                 let list_like_ty = match &*self.unifier.get_ty(value.custom.unwrap()) {
-                    TypeEnum::TList { .. } => self.unifier.add_ty(TypeEnum::TList { ty }),
+                    TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                        let list_tvar = iter_type_vars(params).nth(0).unwrap();
+                        self.unifier
+                            .subst(
+                                self.primitives.list,
+                                &into_var_map([TypeVar { id: list_tvar.id, ty }]),
+                            )
+                            .unwrap()
+                    }
+
                     TypeEnum::TObj { obj_id, .. } if *obj_id == PrimDef::NDArray.id() => {
                         let (_, ndims) =
                             unpack_ndarray_var_tys(self.unifier, value.custom.unwrap());
@@ -1960,13 +2021,20 @@ impl<'a> Inferencer<'a> {
 
                 // the index is not a constant, so value can only be a list-like structure
                 match &*self.unifier.get_ty(value.custom.unwrap()) {
-                    TypeEnum::TList { .. } => {
+                    TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
                         self.constrain(
                             slice.custom.unwrap(),
                             self.primitives.int32,
                             &slice.location,
                         )?;
-                        let list = self.unifier.add_ty(TypeEnum::TList { ty });
+                        let list_tvar = iter_type_vars(params).nth(0).unwrap();
+                        let list = self
+                            .unifier
+                            .subst(
+                                self.primitives.list,
+                                &into_var_map([TypeVar { id: list_tvar.id, ty }]),
+                            )
+                            .unwrap();
                         self.constrain(value.custom.unwrap(), list, &value.location)?;
                         Ok(ty)
                     }
diff --git a/nac3core/src/typecheck/type_inferencer/test.rs b/nac3core/src/typecheck/type_inferencer/test.rs
index 9096ae56..0a367ae7 100644
--- a/nac3core/src/typecheck/type_inferencer/test.rs
+++ b/nac3core/src/typecheck/type_inferencer/test.rs
@@ -139,6 +139,12 @@ impl TestEnvironment {
             fields: HashMap::new(),
             params: VarMap::new(),
         });
+        let list_elem_tvar = unifier.get_fresh_var(Some("list_elem".into()), None);
+        let list = unifier.add_ty(TypeEnum::TObj {
+            obj_id: PrimDef::List.id(),
+            fields: HashMap::new(),
+            params: into_var_map([list_elem_tvar]),
+        });
         let ndarray_dtype_tvar = unifier.get_fresh_var(Some("ndarray_dtype".into()), None);
         let ndarray_ndims_tvar =
             unifier.get_fresh_const_generic_var(uint64, Some("ndarray_ndims".into()), None);
@@ -159,6 +165,7 @@ impl TestEnvironment {
             uint32,
             uint64,
             option,
+            list,
             ndarray,
             size_t: 64,
         };
@@ -273,15 +280,35 @@ impl TestEnvironment {
             fields: HashMap::new(),
             params: VarMap::new(),
         });
+        let list_elem_tvar = unifier.get_fresh_var(Some("list_elem".into()), None);
+        let list = unifier.add_ty(TypeEnum::TObj {
+            obj_id: PrimDef::List.id(),
+            fields: HashMap::new(),
+            params: into_var_map([list_elem_tvar]),
+        });
         let ndarray = unifier.add_ty(TypeEnum::TObj {
             obj_id: PrimDef::NDArray.id(),
             fields: HashMap::new(),
             params: VarMap::new(),
         });
         identifier_mapping.insert("None".into(), none);
-        for (i, name) in ["int32", "int64", "float", "bool", "none", "range", "str", "Exception"]
-            .iter()
-            .enumerate()
+        for (i, name) in [
+            "int32",
+            "int64",
+            "float",
+            "bool",
+            "none",
+            "range",
+            "str",
+            "Exception",
+            "uint32",
+            "uint64",
+            "Option",
+            "list",
+            "ndarray",
+        ]
+        .iter()
+        .enumerate()
         {
             top_level_defs.push(
                 RwLock::new(TopLevelDef::Class {
@@ -299,7 +326,7 @@ impl TestEnvironment {
                 .into(),
             );
         }
-        let defs = 7;
+        let defs = 12;
 
         let primitives = PrimitiveStore {
             int32,
@@ -313,6 +340,7 @@ impl TestEnvironment {
             uint32,
             uint64,
             option,
+            list,
             ndarray,
             size_t: 64,
         };
@@ -424,6 +452,11 @@ impl TestEnvironment {
             "range".into(),
             "str".into(),
             "exception".into(),
+            "uint32".into(),
+            "uint64".into(),
+            "option".into(),
+            "list".into(),
+            "ndarray".into(),
             "Foo".into(),
             "Bar".into(),
             "Bar2".into(),
diff --git a/nac3core/src/typecheck/typedef/mod.rs b/nac3core/src/typecheck/typedef/mod.rs
index 97c9483c..0382830b 100644
--- a/nac3core/src/typecheck/typedef/mod.rs
+++ b/nac3core/src/typecheck/typedef/mod.rs
@@ -13,7 +13,7 @@ use nac3parser::ast::{Location, StrRef};
 use super::type_error::{TypeError, TypeErrorKind};
 use super::unification_table::{UnificationKey, UnificationTable};
 use crate::symbol_resolver::SymbolValue;
-use crate::toplevel::{DefinitionId, TopLevelContext, TopLevelDef};
+use crate::toplevel::{helper::PrimDef, DefinitionId, TopLevelContext, TopLevelDef};
 use crate::typecheck::type_inferencer::PrimitiveStore;
 
 #[cfg(test)]
@@ -207,12 +207,6 @@ pub enum TypeEnum {
         ty: Vec<Type>,
     },
 
-    /// A list type.
-    TList {
-        /// The type of elements present in this list.
-        ty: Type,
-    },
-
     /// An object type.
     TObj {
         /// The [`DefinitionId`] of this object type.
@@ -246,7 +240,6 @@ impl TypeEnum {
             TypeEnum::TVar { .. } => "TVar",
             TypeEnum::TLiteral { .. } => "TConstant",
             TypeEnum::TTuple { .. } => "TTuple",
-            TypeEnum::TList { .. } => "TList",
             TypeEnum::TObj { .. } => "TObj",
             TypeEnum::TVirtual { .. } => "TVirtual",
             TypeEnum::TCall { .. } => "TCall",
@@ -482,9 +475,27 @@ impl Unifier {
                     )
                 }
             }
-            TypeEnum::TList { ty } => self
-                .get_instantiations(*ty)
-                .map(|ty| ty.iter().map(|&ty| self.add_ty(TypeEnum::TList { ty })).collect_vec()),
+            TypeEnum::TObj { obj_id, params, .. } if *obj_id == PrimDef::List.id() => {
+                let tv = iter_type_vars(params).nth(0).unwrap();
+
+                let tv_id = if let TypeEnum::TVar { id, .. } =
+                    self.unification_table.probe_value(tv.ty).as_ref()
+                {
+                    *id
+                } else {
+                    tv.id
+                };
+
+                self.get_instantiations(tv.ty).map(|ty_insts| {
+                    ty_insts
+                        .iter()
+                        .map(|&ty_inst| {
+                            self.subst(ty, &into_var_map([TypeVar { id: tv_id, ty: ty_inst }]))
+                                .unwrap_or(ty)
+                        })
+                        .collect()
+                })
+            }
             TypeEnum::TVirtual { ty } => self.get_instantiations(*ty).map(|ty| {
                 ty.iter().map(|&ty| self.add_ty(TypeEnum::TVirtual { ty })).collect_vec()
             }),
@@ -541,9 +552,7 @@ impl Unifier {
 
             TVar { .. } => allowed_typevars.iter().any(|b| self.unification_table.unioned(a, *b)),
             TCall { .. } => false,
-            TList { ty }
-            | TVirtual { ty } => self.is_concrete(*ty, allowed_typevars),
-
+            TVirtual { ty } => self.is_concrete(*ty, allowed_typevars),
             TTuple { ty } => ty.iter().all(|ty| self.is_concrete(*ty, allowed_typevars)),
             TObj { params: vars, .. } => {
                 vars.values().all(|ty| self.is_concrete(*ty, allowed_typevars))
@@ -885,11 +894,16 @@ impl Unifier {
                 self.unify_impl(x, b, false)?;
                 self.set_a_to_b(a, x);
             }
-            (TVar { fields: Some(fields), range, is_const_generic: false, .. }, TList { ty }) => {
+            (
+                TVar { fields: Some(fields), range, is_const_generic: false, .. },
+                TObj { obj_id, params, .. },
+            ) if *obj_id == PrimDef::List.id() => {
+                let ty = iter_type_vars(params).nth(0).unwrap().ty;
+
                 for (k, v) in fields {
                     match *k {
                         RecordKey::Int(_) => {
-                            self.unify_impl(v.ty, *ty, false).map_err(|e| e.at(v.loc))?;
+                            self.unify_impl(v.ty, ty, false).map_err(|e| e.at(v.loc))?;
                         }
                         RecordKey::Str(_) => {
                             return Err(TypeError::new(TypeErrorKind::NoSuchField(*k, b), v.loc))
@@ -979,12 +993,6 @@ impl Unifier {
                 }
                 self.set_a_to_b(a, b);
             }
-            (TList { ty: ty1 }, TList { ty: ty2 }) => {
-                if self.unify_impl(*ty1, *ty2, false).is_err() {
-                    return Err(TypeError::new(TypeErrorKind::IncompatibleTypes(a, b), None));
-                }
-                self.set_a_to_b(a, b);
-            }
             (TVar { fields: Some(map), range, .. }, TObj { fields, .. }) => {
                 for (k, field) in map {
                     match *k {
@@ -1222,9 +1230,6 @@ impl Unifier {
                     ty.iter().map(|v| self.internal_stringify(*v, obj_to_name, var_to_name, notes));
                 format!("tuple[{}]", fields.join(", "))
             }
-            TypeEnum::TList { ty } => {
-                format!("list[{}]", self.internal_stringify(*ty, obj_to_name, var_to_name, notes))
-            }
             TypeEnum::TVirtual { ty } => {
                 format!(
                     "virtual[{}]",
@@ -1357,9 +1362,6 @@ impl Unifier {
                     None
                 }
             }
-            TypeEnum::TList { ty } => {
-                self.subst_impl(*ty, mapping, cache).map(|t| self.add_ty(TypeEnum::TList { ty: t }))
-            }
             TypeEnum::TVirtual { ty } => self
                 .subst_impl(*ty, mapping, cache)
                 .map(|t| self.add_ty(TypeEnum::TVirtual { ty: t })),
@@ -1370,6 +1372,7 @@ impl Unifier {
                 // This is also used to prevent infinite substitution...
                 let need_subst = params.values().any(|v| {
                     let ty = self.unification_table.probe_value(*v);
+                    // TODO(Derppening): #444
                     if let TypeEnum::TVar { id, .. } = ty.as_ref() {
                         mapping.contains_key(id)
                     } else {
@@ -1526,8 +1529,22 @@ impl Unifier {
                     Ok(None)
                 }
             }
-            (TList { ty: ty1 }, TList { ty: ty2 }) => {
-                Ok(self.get_intersection(*ty1, *ty2)?.map(|ty| self.add_ty(TList { ty })))
+            // TODO(Derppening): #444
+            (
+                TObj { obj_id: id1, fields, params: params1 },
+                TObj { obj_id: id2, params: params2, .. },
+            ) if *id1 == PrimDef::List.id() && *id2 == PrimDef::List.id() => {
+                let tv_id = iter_type_vars(params1).nth(0).unwrap().id;
+                let ty1 = iter_type_vars(params1).nth(0).unwrap().ty;
+                let ty2 = iter_type_vars(params2).nth(0).unwrap().ty;
+
+                Ok(self.get_intersection(ty1, ty2)?.map(|ty| {
+                    self.add_ty(TObj {
+                        obj_id: *id1,
+                        fields: fields.clone(),
+                        params: into_var_map([TypeVar { id: tv_id, ty }]),
+                    })
+                }))
             }
             (TVirtual { ty: ty1 }, TVirtual { ty: ty2 }) => {
                 Ok(self.get_intersection(*ty1, *ty2)?.map(|ty| self.add_ty(TVirtual { ty })))
diff --git a/nac3core/src/typecheck/typedef/test.rs b/nac3core/src/typecheck/typedef/test.rs
index d56a97d8..451f5f01 100644
--- a/nac3core/src/typecheck/typedef/test.rs
+++ b/nac3core/src/typecheck/typedef/test.rs
@@ -32,10 +32,7 @@ impl Unifier {
                 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::TVirtual { ty: ty1 }, TypeEnum::TVirtual { ty: ty2 }) => self.eq(*ty1, *ty2),
             (
                 TypeEnum::TObj { obj_id: id1, params: params1, .. },
                 TypeEnum::TObj { obj_id: id2, params: params2, .. },
@@ -119,6 +116,15 @@ impl TestEnvironment {
                 params: into_var_map([tvar]),
             }),
         );
+        let tvar = unifier.get_dummy_var();
+        type_mapping.insert(
+            "list".into(),
+            unifier.add_ty(TypeEnum::TObj {
+                obj_id: PrimDef::List.id(),
+                fields: HashMap::new(),
+                params: into_var_map([tvar]),
+            }),
+        );
 
         TestEnvironment { unifier, type_mapping }
     }
@@ -133,6 +139,36 @@ impl TestEnvironment {
         // for testing only, so we can just panic when the input is malformed
         let end = typ.find(|c| ['[', ',', ']', '='].contains(&c)).unwrap_or(typ.len());
         match &typ[..end] {
+            "list" => {
+                let mut s = &typ[end..];
+                assert_eq!(&s[0..1], "[");
+                let mut ty = Vec::new();
+                while &s[0..1] != "]" {
+                    let result = self.internal_parse(&s[1..], mapping);
+                    ty.push(result.0);
+                    s = result.1;
+                }
+
+                assert_eq!(ty.len(), 1);
+
+                let list_elem_tvar = if let TypeEnum::TObj { params, .. } =
+                    &*self.unifier.get_ty_immutable(self.type_mapping["list"])
+                {
+                    iter_type_vars(params).next().unwrap()
+                } else {
+                    unreachable!()
+                };
+
+                (
+                    self.unifier
+                        .subst(
+                            self.type_mapping["list"],
+                            &into_var_map([TypeVar { id: list_elem_tvar.id, ty: ty[0] }]),
+                        )
+                        .unwrap(),
+                    &s[1..],
+                )
+            }
             "tuple" => {
                 let mut s = &typ[end..];
                 assert_eq!(&s[0..1], "[");
@@ -144,12 +180,6 @@ impl TestEnvironment {
                 }
                 (self.unifier.add_ty(TypeEnum::TTuple { ty }), &s[1..])
             }
-            "list" => {
-                assert_eq!(&typ[end..=end], "[");
-                let (ty, s) = self.internal_parse(&typ[end + 1..], mapping);
-                assert_eq!(&s[0..1], "]");
-                (self.unifier.add_ty(TypeEnum::TList { ty }), &s[1..])
-            }
             "Record" => {
                 let mut s = &typ[end..];
                 assert_eq!(&s[0..1], "[");
@@ -274,7 +304,7 @@ fn test_unify(
         ("v1", "tuple[int]"),
         ("v2", "list[int]"),
     ],
-    (("v1", "v2"), "Incompatible types: list[0] and tuple[0]")
+    (("v1", "v2"), "Incompatible types: 11[0] and tuple[0]")
     ; "type mismatch"
 )]
 #[test_case(2,
@@ -298,7 +328,7 @@ fn test_unify(
         ("v1", "Record[a=float,b=int]"),
         ("v2", "Foo[v3]"),
     ],
-    (("v1", "v2"), "`3[typevar4]::b` field/method does not exist")
+    (("v1", "v2"), "`3[typevar5]::b` field/method does not exist")
     ; "record obj merge"
 )]
 /// Test cases for invalid unifications.
@@ -388,6 +418,14 @@ fn test_typevar_range() {
     let int_list = env.parse("list[int]", &HashMap::new());
     let float_list = env.parse("list[float]", &HashMap::new());
 
+    let list_elem_tvar = if let TypeEnum::TObj { params, .. } =
+        &*env.unifier.get_ty_immutable(env.type_mapping["list"])
+    {
+        iter_type_vars(params).next().unwrap()
+    } else {
+        unreachable!()
+    };
+
     // unification between v and int
     // where v in (int, bool)
     let v = env.unifier.get_fresh_var_with_range(&[int, boolean], None, None).ty;
@@ -398,7 +436,7 @@ fn test_typevar_range() {
     let v = env.unifier.get_fresh_var_with_range(&[int, boolean], None, None).ty;
     assert_eq!(
         env.unify(int_list, v),
-        Err("Expected any one of these types: 0, 2, but got list[0]".to_string())
+        Err("Expected any one of these types: 0, 2, but got 11[0]".to_string())
     );
 
     // unification between v and float
@@ -410,7 +448,11 @@ fn test_typevar_range() {
     );
 
     let v1 = env.unifier.get_fresh_var_with_range(&[int, boolean], None, None).ty;
-    let v1_list = env.unifier.add_ty(TypeEnum::TList { ty: v1 });
+    let v1_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: v1 }]),
+    });
     let v = env.unifier.get_fresh_var_with_range(&[int, v1_list], None, None).ty;
     // unification between v and int
     // where v in (int, list[v1]), v1 in (int, bool)
@@ -424,9 +466,10 @@ fn test_typevar_range() {
     let v = env.unifier.get_fresh_var_with_range(&[int, v1_list], None, None).ty;
     // unification between v and list[float]
     // where v in (int, list[v1]), v1 in (int, bool)
+    println!("float_list: {}, v: {}", env.unifier.stringify(float_list), env.unifier.stringify(v));
     assert_eq!(
         env.unify(float_list, v),
-        Err("Expected any one of these types: 0, list[typevar5], but got list[1]\n\nNotes:\n    typevar5 ∈ {0, 2}".to_string())
+        Err("Expected any one of these types: 0, 11[typevar6], but got 11[1]\n\nNotes:\n    typevar6 ∈ {0, 2}".to_string())
     );
 
     let a = env.unifier.get_fresh_var_with_range(&[int, float], None, None).ty;
@@ -441,34 +484,66 @@ fn test_typevar_range() {
 
     let a = env.unifier.get_fresh_var_with_range(&[int, float], None, None).ty;
     let b = env.unifier.get_fresh_var_with_range(&[boolean, float], None, None).ty;
-    let a_list = env.unifier.add_ty(TypeEnum::TList { ty: a });
+    let a_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: a }]),
+    });
     let a_list = env.unifier.get_fresh_var_with_range(&[a_list], None, None).ty;
-    let b_list = env.unifier.add_ty(TypeEnum::TList { ty: b });
+    let b_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: b }]),
+    });
     let b_list = env.unifier.get_fresh_var_with_range(&[b_list], None, None).ty;
     env.unifier.unify(a_list, b_list).unwrap();
-    let float_list = env.unifier.add_ty(TypeEnum::TList { ty: float });
+    let float_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: float }]),
+    });
     env.unifier.unify(a_list, float_list).unwrap();
     // previous unifications should not affect a and b
     env.unifier.unify(a, int).unwrap();
 
     let a = env.unifier.get_fresh_var_with_range(&[int, float], None, None).ty;
     let b = env.unifier.get_fresh_var_with_range(&[boolean, float], None, None).ty;
-    let a_list = env.unifier.add_ty(TypeEnum::TList { ty: a });
-    let b_list = env.unifier.add_ty(TypeEnum::TList { ty: b });
+    let a_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: a }]),
+    });
+    let b_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: b }]),
+    });
     env.unifier.unify(a_list, b_list).unwrap();
-    let int_list = env.unifier.add_ty(TypeEnum::TList { ty: int });
+    let int_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: int }]),
+    });
     assert_eq!(
         env.unify(a_list, int_list),
-        Err("Incompatible types: list[typevar22] and list[0]\
-            \n\nNotes:\n    typevar22 ∈ {1}"
+        Err("Incompatible types: 11[typevar23] and 11[0]\
+            \n\nNotes:\n    typevar23 ∈ {1}"
             .into())
     );
 
     let a = env.unifier.get_fresh_var_with_range(&[int, float], None, None).ty;
     let b = env.unifier.get_dummy_var().ty;
-    let a_list = env.unifier.add_ty(TypeEnum::TList { ty: a });
+    let a_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: a }]),
+    });
     let a_list = env.unifier.get_fresh_var_with_range(&[a_list], None, None).ty;
-    let b_list = env.unifier.add_ty(TypeEnum::TList { ty: b });
+    let b_list = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: b }]),
+    });
     env.unifier.unify(a_list, b_list).unwrap();
     assert_eq!(
         env.unify(b, boolean),
@@ -482,16 +557,25 @@ fn test_rigid_var() {
     let a = env.unifier.get_fresh_rigid_var(None, None).ty;
     let b = env.unifier.get_fresh_rigid_var(None, None).ty;
     let x = env.unifier.get_dummy_var().ty;
-    let list_a = env.unifier.add_ty(TypeEnum::TList { ty: a });
-    let list_x = env.unifier.add_ty(TypeEnum::TList { ty: x });
+    let list_elem_tvar = env.unifier.get_fresh_var(Some("list_elem".into()), None);
+    let list_a = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: a }]),
+    });
+    let list_x = env.unifier.add_ty(TypeEnum::TObj {
+        obj_id: env.type_mapping["list"].obj_id(&env.unifier).unwrap(),
+        fields: Mapping::default(),
+        params: into_var_map([TypeVar { id: list_elem_tvar.id, ty: x }]),
+    });
     let int = env.parse("int", &HashMap::new());
     let list_int = env.parse("list[int]", &HashMap::new());
 
-    assert_eq!(env.unify(a, b), Err("Incompatible types: typevar3 and typevar2".to_string()));
+    assert_eq!(env.unify(a, b), Err("Incompatible types: typevar4 and typevar3".to_string()));
     env.unifier.unify(list_a, list_x).unwrap();
     assert_eq!(
         env.unify(list_x, list_int),
-        Err("Incompatible types: list[typevar2] and list[0]".to_string())
+        Err("Incompatible types: 11[typevar3] and 11[0]".to_string())
     );
 
     env.unifier.replace_rigid_var(a, int);
@@ -506,10 +590,21 @@ fn test_instantiation() {
     let float = env.parse("float", &HashMap::new());
     let list_int = env.parse("list[int]", &HashMap::new());
 
-    let obj_map: HashMap<_, _> = [(0usize, "int"), (1, "float"), (2, "bool")].into();
+    let list_elem_tvar = if let TypeEnum::TObj { params, .. } =
+        &*env.unifier.get_ty_immutable(env.type_mapping["list"])
+    {
+        iter_type_vars(params).next().unwrap()
+    } else {
+        unreachable!()
+    };
+
+    let obj_map: HashMap<_, _> = [(0usize, "int"), (1, "float"), (2, "bool"), (11, "list")].into();
 
     let v = env.unifier.get_fresh_var_with_range(&[int, boolean], None, None).ty;
-    let list_v = env.unifier.add_ty(TypeEnum::TList { ty: v });
+    let list_v = env
+        .unifier
+        .subst(env.type_mapping["list"], &into_var_map([TypeVar { id: list_elem_tvar.id, ty: v }]))
+        .unwrap();
     let v1 = env.unifier.get_fresh_var_with_range(&[list_v, int], None, None).ty;
     let v2 = env.unifier.get_fresh_var_with_range(&[list_int, float], None, None).ty;
     let t = env.unifier.get_dummy_var().ty;
@@ -536,7 +631,7 @@ fn test_instantiation() {
         tuple[int, list[bool], list[int]]
         tuple[int, list[int], float]
         tuple[int, list[int], list[int]]
-        v5"
+        v6"
     }
     .split('\n')
     .collect_vec();