Tokenizer functional, fragile parsing

atom.py

@@ -1,2 +1,13 @@
 class Atom:
-	pass
+    car: Atom | int | str | bool | None
+    cdr: Atom | None
+
+    def __init__(self, car: Atom|int|str|bool|None, cdr: Atom|None):
+        self.car = car
+        self.cdr = cdr
+
+    def setval(self, atom: Atom | int | str | bool | None):
+        self.car = atom
+
+    def append(self, atom: Atom):
+        self.cdr = atom

lisp.py

@@ -1,5 +1,9 @@
 import atom
+import reader
 
 class Lisp:
+	def parse(self, expression):
+		return reader.tokenize(expression)
+
 	def evaluate(self, expression: str):
-		return expression.upper()
+		return self.parse(expression)

reader.py

@@ -0,0 +1,51 @@
+import re
+from typing import Any
+import lisp
+import atom
+
+
+class Reader:
+    tokens: list[str|Any]
+
+    def __init__(self):
+        self.tokens = []
+        self.interpreter = lisp.Lisp()
+
+    def tokenize(self, expression: str):
+        self.tokens += re.findall(r"""[\s,]*[;.*]*([()']|"(?:\\.|[^\\"])*"?|[^\s()'",;]*)""", expression)
+        while self.peek() != "":
+            self.read_expression()
+        self.consume()
+
+    def peek(self):
+        return self.tokens[0]
+
+    def consume(self):
+        token = self.tokens[0]
+        self.tokens = self.tokens[1:]
+        return token
+
+    def read_expression(self) -> atom.Atom | None:
+        if len(self.tokens) == 0:
+            return None
+        if self.peek() == "(":
+            self.consume()
+            return self.read_list()
+        else:
+            return self.read_atom()
+
+    def read_list(self):
+        token = self.peek()
+        last = atom.Atom(None, None)
+        first = last
+        while token != ")":
+            last.setval(self.read_expression())
+            last.append(atom.Atom(None, None))
+            last = last.cdr
+            token = self.peek()
+        self.consume()
+        return first
+
+    def read_atom(self) -> atom.Atom:
+        print(self.peek())
+        return atom.Atom(self.consume(), None)

repl.py

@@ -1,12 +1,12 @@
-import lisp
+import reader
 
 def main():
 	print("Welcome message.")
-	state = lisp.Lisp()
+	interpreter = reader.Reader()
 	# REPL Loop
 	while True:
 		expression: str = input("> ")
-		print(state.evaluate(expression))
+		interpreter.tokenize(expression)
 
 if __name__ == "__main__":
 	main()