On Mon, 9 Aug 2021, Hans van der Meer via ntg-context wrote:
> In the TeX to Lua interface with
>
> \def\Macro#1{\directlua{luafunction("#1")}}
>
> the transfer from TeX to Lua is by string. However what to do at the Lua end
> when calling \Macro{}?
> As I understand it, then on the Lua side an empty argument and an empty
> string are indistinguishable.
That is not the case:
$ echo 'print("" == nil)' | lua
false
> This is not always wanted, for example when one needs to place either a nil
> or an empty string into a Lua table. I am running in trouble when to t.key
> set to \Macro{} should become nil or when it should become "".
If you call luafunction(""), the string is empty and not nil.
\startluacode
userdata = userdata or {}
function userdata.macro(str)
if str == nil then
context("Argument is nil")
elseif str == "" then
context("Argument is empty")
else
context("Argument is %s", str)
end
end
\stopluacode
\define[1]\Macro{\ctxlua{userdata.macro([==[#1]==])}}
\starttext
\startlines
\Macro{}
\Macro{ABC}
\ctxlua{userdata.macro()}
\stoplines
\stoptext
Aditya
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