[Proposal] Support "inf", "-inf" and "-nan" in tonumber()

[Martin Eden]

Current Lua implementation of tonumber() does not handle values
"inf", "-inf" and "-nan" for string that supposed to be number value.

But tostring() function produces them:

  Lua 5.5.0  Copyright (C) 1994-2025 Lua.org, PUC-Rio
  > tostring(1/0)
  inf
  > tostring(-1/0)
  -inf
  > tostring(0/0)
  -nan

So tostring() value is useless for decoding number using tonumber():

  > tonumber(tostring(1/0))
  nil

-- Martin

[Yao Zi]

"%q" specifier of string.format() guarantees the result could be safely
read back by the interpreter, including inf and -inf ("1e9999" and
"-1e9999" are returned respectively). However, for NaN it returns
"(0/0)" which could be evaluated by interpreter but not parsed by
tonumber(), either...

> -- Martin

Regards,
Yao Zi

[Philippe Verdy]

IMHO these special formats returned by '%q' are just non-sense "hacks" (they target the behavior of some specific current Lua parser versions, and still the same parsers cannot handle "-nan", "-inf" and "+inf" returned by the common tostring() serializer intended for humans and for interoperable data formats).
What the Lua parser does for its own language syntax (and for the special '%q' format) should not be exposed into tonumber()/tostring() (and the common '%f' format) that should work interoperably (possibly with i18n linguistic support).

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