Question regarding Lisp_Object representation of symbols

[Gerd Möllmann]

Symbols are currently encoded as words with tag = 0 (= Lisp_Symbol
enumerator), that when untagged are an offset from lispsym (the array of
built-in symbols), not a pointer to some structure like it is done for
other Lisp types. That makes the word 0x0 = Qnil, 0x1 = Qt, and so on.

My question comes from playing with another GC library, where this
unique encoding is, well, quite inconvenient. So, I'd like to ask two
questions:

- Does someone remember the reasons why this has been done?

- Is there something that relies on this? Maybe something that
  relies on 0x0 being a valid Lisp_Object?

Thanks!