Re: [NTG-context] How to get parameters in lua

20 Sep 2014

      On 9/19/2014 9:30 AM, Christoph Reller wrote:
...
...
Hi,
\installcommandhandler nicely provides (among others) \define<name> and
\setup<name> commands. Thus it is easy to provide a key with
\setup<name>[key=value] and to read the value of such a key with
\<name>parameter{key}.
My question is: How do I read the value of a key defined with
\setup...[key=value] on the lua side? If I use
   context.<name>parameter("key")
then the value of key is printed directly. I want to be able to read
that value and use it in lua with something like
   myvariable = context.?whatfunction?("key")
Here is some example code:
\unprotect
\startluacode
   function myfun(parameters,content)
     context("From lua: Parameters: ")
     context(parameters)
     context.elemparameter("gkey") -- directly prints the parameter
     context.par()
   end
\stopluacode
\installnamespace{elem}
\installcommandhandler \????elem {elem} \????elem
\appendtoks
   \setuevalue{\currentelem}{\elem_cmd{\currentelem}}%
\to \everydefineelem
\unexpanded\def\elem_cmd#environment{%
   \edef\currentelem{#environment}%
   \dosingleempty\elem_cmd_parameters}
\def\elem_cmd_parameters[#parameters]#content{%
   \setupcurrentelem[#parameters]
   From \TeX\: Parameters: key=\elemparameter{key},
gkey=\elemparameter{gkey}\par
\ctxlua{myfun(\!!bs#parameters\!!es,\!!bs\normalunexpanded{#content}\!!es)}
...
}
\defineelem[base]
\setupelem[gkey=gval]
\protect
\starttext
\base[key=val]{Hello}
\stoptext
Thank you for any feedback,
On Fri, Sep 19, 2014 at 12:00 PM, Hans Hagen wrote:
...
something like this ... keep in mind that there is no grouping in lua
% macros=mkvi
\unprotect
\installnamespace{elem}
\installcommandhandler \????elem {elem} \????elem
\startluacode
     userdata.elem = { data = { [""] = { } } }
function userdata.elem.define(namespace,parent)
         print("define",namespace,parent)
         userdata.elem.data[namespace] = { }
         if namespace ~= parent then
table.setmetatableindex(userdata.elem.data[namespace],userdata.elem.data[parent])
...
end
     end
function userdata.elem.setup(namespace,key,gkey)
         print("setup",namespace,key,gkey)
         userdata.elem.data[namespace].key = key
         userdata.elem.data[namespace].gkey = gkey
     end
function userdata.myfun(namespace,one,two)
         context.par()
         context("elem: one=%s",userdata.elem.data[namespace][one])
         context.par()
         context("elem: two=%s",userdata.elem.data[namespace][two])
         context.par()
     end
\stopluacode
\appendtoks
     \setuevalue{\currentelem}{\elem_cmd{\currentelem}}%
     \ctxlua{userdata.elem.define("\currentelem","\currentelemparent")}%
\to \everydefineelem
\appendtoks
\ctxlua{userdata.elem.setup("\currentelem","\elemparameter{key}","\elemparameter{gkey}")}%
...
\to \everysetupelem
\unexpanded\def\elem_cmd#environment%
   {\edef\currentelem{#environment}%
    \dosingleempty\elem_cmd_parameters}
\def\elem_cmd_parameters[#parameters]#content%
   {\setupelem[\currentelem][#parameters]
    From \TeX\: Parameters: key=\elemparameter{key},
gkey=\elemparameter{gkey}\par
    \ctxlua{userdata.myfun("\currentelem","key","gkey")}}
\defineelem[base]
\setupelem[gkey=gval]
\protect
\starttext
\base[key=val]{Hello}
\stoptext
A simpler alternative is:
% macros=mkvi
\unprotect
\installnamespace{elem}
\installcommandhandler \????elem {elem} \????elem
\startluacode
     userdata.elem = { data = {  } }
function userdata.elem.sync(key,gkey)
         userdata.elem.data.key = key
         userdata.elem.data.gkey = gkey
     end
function userdata.myfun(one,two)
         context.par()
         context("elem: one=%s",userdata.elem.data[one])
         context.par()
         context("elem: two=%s",userdata.elem.data[two])
         context.par()
     end
\stopluacode
\appendtoks
     \setuevalue{\currentelem}{\elem_cmd{\currentelem}}%
\to \everydefineelem
\unexpanded\def\elem_cmd#environment%
   {\edef\currentelem{#environment}%
    \dosingleempty\elem_cmd_parameters}
\unexpanded\def\elem_sync
{\ctxlua{userdata.elem.sync("\elemparameter{key}","\elemparameter{gkey}")}}
...
\def\elem_cmd_parameters[#parameters]#content%
   {\setupcurrentelem[#parameters]
    \elem_sync
    From \TeX\: Parameters: key=\elemparameter{key},
gkey=\elemparameter{gkey}\par
    \ctxlua{userdata.myfun("key","gkey")}}
\defineelem[base]
\setupelem[gkey=gval]
\protect
\starttext
\base[key=val]{Hello}
\stoptext
Thank you Hans!

Two general questions arise (if your permit):

1. Where are the key-value pairs stored?
In your first solution you handle the key setting by explicitly calling lua
on every \setup<name> call.  It seems that all key-value pairs (that are
set with \installcommandhandler-generated \setup<name>) are stored on the
TeX side and not on the lua side.  Is this correct?

2. Calling \ctxlua from lua.
I was tempted to add another level of indirection to your second (the
"synchronize") solution.  I.e: in the lua code (in a separate lua file to
avoid the do ... end introduced by \startluacode ... \stopluacode) I have:

n = ""
v = ""
function getkey(name,value)
   n = name
   v = value
end
function myfun(parameters,content)
   context([[\ctxlua{getkey("gkey","\elemparameter{gkey}")}]])
   context(" name=")
   context(n)
   context(", value=")
   context(v)
end

The above does not work because the value obtained "lags behind", i.e.
initially v will be "", on the second call v will have the value of the
first \setupelem[gkey=gval], and so on.  I guess this lag is due to the way
TeX and lua communicate to each other?

A small question: What do you mean by "there is no grouping in lua"?

Thank you anyway for your valuable input.

Regards, Christoph