diff --git a/compiler/lexer.py b/compiler/lexer.py
index 8bc37ef..fececbd 100644
--- a/compiler/lexer.py
+++ b/compiler/lexer.py
@@ -25,6 +25,10 @@ class Token:
     def __repr__(self):
         return f"{self.kind.name}({repr(self.value)})"
 
+    @property
+    def pure(self) -> bool:
+        return True
+
 
 class Tokens(enum.Enum):
     Integer = re.compile(r"[0-9]+")