nil from TeX to Lua

nil from TeX to Lua

[Hans van der Meer via ntg-context]

[-- Attachment #1.1: Type: text/plain, Size: 602 bytes --]

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. 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 "".
Is there some common understanding about how to handle this situation?

dr. Hans van der Meer



[-- Attachment #1.2: Type: text/html, Size: 2151 bytes --]

[-- Attachment #2: Type: text/plain, Size: 493 bytes --]

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________

Re: nil from TeX to Lua

[Aditya Mahajan via ntg-context]

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
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________

Re: nil from TeX to Lua

[Taco Hoekwater via ntg-context]

> On 9 Aug 2021, at 22:05, Aditya Mahajan via ntg-context <ntg-context@ntg.nl> wrote:
> 
> 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. 
> 

On the TeX side, these are always indistinguishable (as TeX doesn’t have ’strings’) so depending
on the called macro, you could just assume str == "” actually means nil?

But a clearer example of where you run into trouble would be helpful.

Best wishes,
Taco


— 
Taco Hoekwater              E: taco@bittext.nl
genderfluid (all pronouns)



___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________

Re: nil from TeX to Lua

[Hans Hagen via ntg-context]

On 8/10/2021 9:23 AM, Taco Hoekwater via ntg-context wrote:
> 
> 
>> On 9 Aug 2021, at 22:05, Aditya Mahajan via ntg-context <ntg-context@ntg.nl> wrote:
>>
>> 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.
>>
> 
> On the TeX side, these are always indistinguishable (as TeX doesn’t have ’strings’) so depending
> on the called macro, you could just assume str == "” actually means nil?

indeed, just check for ""

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________