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