from dataclasses import dataclass
from typing import Union


class LexError(Exception):
    pass


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


def tokenize(src: str) -> list:
    tokens = []
    i = 0
    n = len(src)
    while i < n:
        ch = src[i]
        if ch in ' \t':
            i += 1
        elif 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
        elif 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
        else:
            raise LexError(f"unexpected character {ch!r} at position {i}")
    tokens.append(Token('EOF'))
    return tokens