Section 2.2 of my 5.1 manual states:
[...]
There are 8 basic types in Lua: nil, boolean, number, string
function, userdata, thread and table.
Nil is the type of the value nil, whose main property is to be
different from any other value; it usually represents the
absence of a useful value.
[...]
Typing in that portion of the manual by hand, I tend to feel that
there is tension between an "implicit nil" and an "explicit nil",
with "implicit nil" possibly being the best description for:
tostring(f())
Another name for "implicit nil" might be "none", which links into the
discussion thread descriptions and the C API. You could even split
"none" into two variants (the naming here is awkward, sorry):
In other words,
none-that-will-coerce-to-nil-upon-evaluation
none-that-cannot-be-coerced-to-nil
Exactly!
For some strange reason, Lua is not conceptually clear about nil.
Nil is defined as absence of value.
And this definition works well with Lua tables (all absent keys have value nil).
This definition works well also with multiple assignment in Lua.
But tuples in Lua are inconsistent with the definition of nil.
IMO, any tuple of values should be think of as padded by nils to infinity.
There should not be any difference between the following statements:
return
return nil
return nil, nil
Neither in Lua, nor in C API a user should be able to distinguish between LUA_TNONE and LUA_TNIL.
