Infinity as index

["Lukas Prokop" <admin@...>]

Hi,

I don't know whether this was thought through in any way, but lua defines
+inf and -inf as well as not-a-number.

    Lua 5.2.3  Copyright (C) 1994-2013 Lua.org, PUC-Rio
    > return math.huge
    inf
    > return 1/0
    inf
    > return 0/0
    -nan

Of course, we can negate it as well (except for nan)

    > return -math.huge
    -inf
    > return -1/0
    -inf
    > return -0/0
    -nan

Now my point is that we can use this as indices. My intuition tells me the
following:

    -nan  - behaves like a nil as index or throws error (number expected)
    inf   - behaves like the end of a sequence as index
    -inf  - behaves like the beginning of a sequence as index

I guess -inf and nan behave as expected, because of checks like

    if (init < 1) init = 1;

in lstrlib.c, but inf does not:

    > return  string.find("asd", "a", 1/0)
    1     1

Thus, inf behaves like "nil" or "0". This is against my intuition. What is
your opinion?

best regards,
meisterluk

[0] https://twitter.com/meisterluk/status/457946586778464257
[1] A patch has to provided somewhere between lstrlib.c in function
str_find_aux line 582 and lapi.c in function lua_tointegerx line 349.
Somehow I only received a "1" from optinteger for the infinity value. This
got me confused.