List of calling modes in ConTeXt document

Question

I need something in document like this

\listcallingmodes

which return the list of calling modes, that is, if I run

context --mode=mode1,mode2 file.tex

in file.tex:

\starttext
\startmode[a1]
This is mode a1
\stopmode
Hello
\listcallingmodes
\stoptext

which I would to get

Hellp
mode1 mode2

Note that in this file we could have other modes than calling modes

Answer 1

NEW ANSWER:

If you only need those modes called via the command line, this task is easier. Since ConTeXt stores command line data in the environment namespace, let's take advantage of this:

\startluacode
local listofcalledmodes = function()
    local split = string.split
    local flag  = '^--c:mode='
    local concat = table.concat
    for _, v in pairs(environment.originalarguments) do
        if v:find(flag) then
            local w = split(v:gsub(flag, ""), ",")
            context(concat(w, " ")) 
            return  
        end
    end
    context("No modes set")
end
interfaces.implement{
    name   = "listofcalledmodes",
    public = true,
    actions = listofcalledmodes
}
\stopluacode
\starttext
\startTEXpage
My list of modes: \listofcalledmodes
\stopTEXpage
\stoptext

Compiling your file the following way (159.tex is my file):

context --mode=amode,anothermode,toomanymodes 159.tex

I get the following result:

OLD ANSWER:

I'll ask for a feature request to the mailing list so a proper macro is available. In the meantime, the following should do the work most of times. Since modes are registered at the TeX end with as command sequences named with a mode> prefix (in core-env.mkiv and core-env.mkxl), we can look up at them in tex.hashtokens (related discussion here). However, if I get you right, you don't want system modes (internal, marked with an asterisk), so they will be filtered out:

\startluacode
local function listofmodes()
    local s1, s2  = "^mode>[^%*]+", "^mode>"
    context.blank() -- change this ad libitum
    for _, v in pairs(tex.hashtokens()) do
        if v:find(s1) and tex.modes[v:gsub(s2, "")] then
            context(v:gsub(s2, ""))
            context.par() -- also change this if needed
        end
    end
end
interfaces.implement{
    name    = "listofmodes",
    public  = true,
    actions = listofmodes
}
\stopluacode
\starttext
Hi, there's a list of used modes: \listofmodes
\stoptext

However, you may need a workaround, setting hash_extra=0 in some cases (issue discussed here), so you're warned.