from dataclasses import dataclass
from typing import List


class LexError(Exception):
    pass


@dataclass
class Token:
    kind: str
    value: object


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


def tokenize(src: str) -> List[Token]:
    tokens: List[Token] = []
    i = 0
    while i < len(src):
        ch = src[i]
        if ch in ' \t\n\r':
            i += 1
            continue
        if ch.isdigit() or ch == '.':
            j = i
            while j < len(src) and (src[j].isdigit() or src[j] == '.'):
                j += 1
            raw = src[i:j]
            try:
                value = float(raw) if '.' in raw else int(raw)
            except ValueError:
                raise LexError(f"invalid number literal {raw!r} at position {i}")
            tokens.append(Token('NUMBER', value))
            i = j
            continue
        if ch in _SINGLE:
            tokens.append(Token(_SINGLE[ch], ch))
            i += 1
            continue
        raise LexError(f"unexpected character {ch!r} at position {i}")
    tokens.append(Token('EOF', None))
    return tokens