from __future__ import annotations
from dataclasses import dataclass
from typing import Union


class LexError(Exception):
    pass


@dataclass
class Token:
    kind: str
    value: Union[int, float, str, None]


def tokenize(src: str) -> list[Token]:
    tokens: list[Token] = []
    i = 0
    n = len(src)
    while i < n:
        ch = src[i]
        if ch in ' \t\r\n':
            i += 1
            continue
        if ch.isdigit() or ch == '.':
            j = i
            while j < n and src[j].isdigit():
                j += 1
            if j < n and src[j] == '.':
                j += 1
                while j < n and src[j].isdigit():
                    j += 1
                tokens.append(Token('NUMBER', float(src[i:j])))
            else:
                tokens.append(Token('NUMBER', int(src[i:j])))
            i = j
            continue
        if ch == '+':
            tokens.append(Token('PLUS', '+'))
        elif ch == '-':
            tokens.append(Token('MINUS', '-'))
        elif ch == '*':
            tokens.append(Token('STAR', '*'))
        elif ch == '/':
            tokens.append(Token('SLASH', '/'))
        elif ch == '(':
            tokens.append(Token('LPAREN', '('))
        elif ch == ')':
            tokens.append(Token('RPAREN', ')'))
        else:
            raise LexError(f"unexpected character {ch!r} at position {i}")
        i += 1
    tokens.append(Token('EOF', None))
    return tokens