# Re: [NTG-context] Code lua in a table

```Dear Hans,

Thank you for new methods!
It would take some time for me to understand them fully.```
```
Learning Lua, metafun, lmtx, wiki is always a challenge for me.
I also wonder where is the boundary of ConTeXt.

I hope that you and all members in this list are well from COVID-19.

Thank you again.

Best regards,

Dalyoung

> 2020. 7. 20. 오후 5:36, Hans Hagen <j.ha...@xs4all.nl> 작성:
>
> On 7/20/2020 7:56 AM, Jeong Dal wrote:
>> Dear Fabrice,
>> You may split Binom(n,k) function into two functions as following:
> > see original mail
> >
>> Dalyoung
> Best stay in a protected namespace ...
>
> \startluacode
>
>    local function fact (n)
>        if n <= 0 then
>            return 1
>        else
>            return n * fact(n-1)
>        end
>    end
>
>    local function ncr(n,r)
>        return fact(n)/(fact(r)*fact(n-r))
>    end
>
>    userdata.P = {
>        fact = fact,
>        ncr  = ncr,
>    }
>
>    function MP.pascal_ncr(n, r)
>        mp.print(ncr(n,r))
>    end
>
> \stopluacode
>
> Watch the last definition. This permits
>
>      % tt := lua("mp.print(userdata.P.ncr(" & decimal n & "," & decimal r & "
> ))");
>
> replaced by
>
>        tt := lua.MP.pascal_ncr(n,r);
>
> which looks nicer.
>
> \startbuffer[pt1]
>    numeric n, r, s, u, dx, dy, tt;
>    path p, q;
>    pair A, B, start, now;
>    u := 1.8cm;
>    A := dir(210)*u;
>    B := dir(-30)*u;
>    dy := sind(30)*u;
>    dx := 2*cosd(30)*u;
>    for n=0 upto 4:
>        start := n*dir(210)*u;
>        for r=0 upto n:
>            s := n-r;
>          % tt := lua("mp.print(userdata.P.ncr(" & decimal n & "," & decimal r
> & " ))");
>          tt := lua.MP.pascal_ncr(n,r);
>            now := start+r*right*dx;
>            dotlabel.top(textext("\$\displaystyle {" & decimal n & "\choose" &
> decimal r & "} = "& decimal tt & "\$"),now);
>            draw (now+A) -- now -- (now+B);
>        endfor;
>    endfor;
> \stopbuffer
>
> Now, in context lmtx we can have a different kind of abstraction. We can do
> this:
>
>    function MP.pascal_ncr_x()
>        mp.print(ncr(mp.scan.pair()))
>    end
>
> and then use:
>
>    tt := runscript("MP.pascal_ncr_x()") (n,r) ;
>
> Of course one can decide to pick to two numerics instead, like
>
>    tt := runscript("MP.pascal_ncr_x()") n r ;
>
> but i leave that as exercise.
>
>          % tt := runscript mp_pascal_ncr (n,r) ;
>            tt := pascal_ncr (n,r) ;
>
> However, we still have the rather verbose runscript here, so we go further,
> we register pascal as script:
>
> \startluacode
>    metapost.registerscript("pascal_ncr",MP.pascal_ncr_x)
> \stopluacode
>
> And then define an alias at the metafun end:
>
> \startMPextensions
>    newinternal mp_pascal_ncr ; mp_pascal_ncr := scriptindex "pascal_ncr" ;
>
>    def pascal_ncr =
>        runscript mp_pascal_ncr
>    enddef ;
> \stopMPextensions
>
> The internal permits this:
>
>   tt := runscript mp_pascal_ncr (n,r) ;
>
> while the additional def permits
>
>            tt := pascal_ncr (n,r) ;
>
> Now watch out, because we define pascal_ncr here, something
> lua.MP.pascal_ncr(n,r) won't work because the last part gets expanded because
> that is what mp does (i'll probably cook something for that some day).
>
> Now, to come back to
>
>   "I couldn’t wikify it at that time because I don’t know
>    how to.  I’ll do it soon."
>
> looks like you suddenly have an additional challenge,
>
> 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
> -----------------------------------------------------------------

___________________________________________________________________________________