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.isdigit() or ch == '.':
            j = i
            has_dot = False
            while j < len(src) and (src[j].isdigit() or (src[j] == '.' and not has_dot)):
                if src[j] == '.':
                    has_dot = True
                j += 1
            raw = src[i:j]
            value = float(raw) if has_dot else int(raw)
            tokens.append(Token('NUMBER', value))
            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