diff --git a/compiler/semantic.py b/compiler/semantic.py
index 53f4cc6..0c6c337 100644
--- a/compiler/semantic.py
+++ b/compiler/semantic.py
@@ -1,13 +1,17 @@
 from __future__ import annotations
 
+import abc
+from typing import Literal
+
 from . import nodes
 from .logger import Logger
+from .typechecking import typecheck
 
 logger = Logger(__name__)
 
 
-class Variable:
-    def __init__(self, context: Context, name: str, value: nodes.Value | None = None):
+class SymbolABC(abc.ABC):
+    def __init__(self, context: Context, name: str, value: nodes.Value | None | Literal["builtin"] = None):
         self.context = context
         self.name = name
         self.definitions = [value]
@@ -23,11 +27,25 @@ class Variable:
         if self._repr_guard:
             return str(self)
         self._repr_guard = True
-        definitions = [str(d.location().begin) for d in self.definitions]
+        definitions = [str(d.location().begin) for d in self.definitions if d is not None]
         self._repr_guard = False
         return f"{str(self)} [definitions: {', '.join(definitions)}]"
 
 
+class Type(SymbolABC):
+    def __init__(self, context: Context, name: str, value: nodes.Value | None | Literal["builtin"] = None):
+        super().__init__(context, name, value)
+
+
+class Variable(SymbolABC):
+    @typecheck
+    def __init__(self, context: Context, name: str, value: nodes.Value | None = None):
+        super().__init__(context, name, value)
+
+    def __str__(self):
+        return f"{self.__class__.__name__}({self.name})"
+
+
 class Context:
     _id_sequence = 0