from dataclasses import dataclass
from typing import Union


class LexError(Exception):
    pass


@dataclass
class Token:
    kind: str
    value: Union[int, float, str]


_SINGLE = {'+': 'PLUS', '-': 'MINUS', '*': 'STAR', '/': 'SLASH',
           '(': 'LPAREN', ')': 'RPAREN'}


def tokenize(src: str) -> list:
    tokens = []
    i = 0
    n = len(src)
    while i < n:
        ch = src[i]
        if ch in ' \t\n\r':
            i += 1
        elif ch in _SINGLE:
            tokens.append(Token(_SINGLE[ch], ch))
            i += 1
        elif ch.isdigit() or ch == '.':
            j = i
            has_dot = False
            while j < n and (src[j].isdigit() or (src[j] == '.' and not has_dot)):
                if src[j] == '.':
                    has_dot = True
                j += 1
            raw = src[i:j]
            try:
                value = float(raw) if has_dot else int(raw)
            except ValueError:
                raise LexError(f"invalid number {raw!r} at position {i}")
            tokens.append(Token('NUMBER', value))
            i = j
        else:
            raise LexError(f"unexpected character {ch!r} at position {i}")
    tokens.append(Token('EOF', ''))
    return tokens