They do e.g. Python

    >>> 0x_ab_cd_01_23
    2882339107

    >>> 0b_0010_0100
    36

TL;DR is that it's because C++ uses quote. The reason C++ uses quote (they considered underscore) is because of a very obscure feature of C++ called custom literal suffixes which I'd never even heard of, but numbers can be suffixed with a custom identifier, and since single underscore is a valid identifier you can't use that. (https://en.cppreference.com/w/cpp/language/user_literal)

[1] https://elixir-lang.org/getting-started/binaries-strings-and...

    0xde_ad_be_ef_00

(Given they have been listed separately rather than as a single number).

Here's how we ended up supporting byte strings (# prefix) in Ecstasy, in this case multi-line:

    Byte[] bytes = #|12 34 56
                    |78 9a BC
                    |dE f0
                   ;

    console.println($|bytes=
                     |{bytes.toHexDump(4)}
                   );

  bytes=
  00: 12 34 56 78 .4Vx
  04: 9A BC DE F0 .¼Þð