import re
from dataclasses import dataclass
from typing import Union


class LexError(Exception):
    pass


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

    def __repr__(self):
        return f"{self.kind}({self.value!r})"


_NUMBER_RE = re.compile(r'\d+\.?\d*|\.\d+')

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


def tokenize(src: str) -> list:
    tokens = []
    i = 0
    while i < len(src):
        ch = src[i]
        if ch in ' \t':
            i += 1
            continue
        m = _NUMBER_RE.match(src, i)
        if m:
            raw = m.group()
            value = float(raw) if '.' in raw else int(raw)
            tokens.append(Token('NUMBER', value))
            i = m.end()
            continue
        if ch in _SINGLE:
            tokens.append(Token(_SINGLE[ch], None))
            i += 1
            continue
        raise LexError(f"unexpected character {ch!r} at position {i}")
    tokens.append(Token('EOF', None))
    return tokens