From: Aditya Mahajan via ntg-context <ntg-context@ntg.nl>
To: Hans van der Meer via ntg-context <ntg-context@ntg.nl>
Cc: Aditya Mahajan <adityam@umich.edu>
Subject: Re: nil from TeX to Lua
Date: Mon, 9 Aug 2021 16:05:46 -0400 (EDT) [thread overview]
Message-ID: <nycvar.YAK.7.78.908.2108091600320.772146@nqv-guvaxcnq> (raw)
In-Reply-To: <C6D68B1B-C07B-44C0-9828-5E4B4069E148@ziggo.nl>
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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next prev parent reply other threads:[~2021-08-09 20:05 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-09 19:58 Hans van der Meer via ntg-context
2021-08-09 20:05 ` Aditya Mahajan via ntg-context [this message]
2021-08-10 7:23 ` Taco Hoekwater via ntg-context
2021-08-10 7:59 ` Hans Hagen via ntg-context
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