Re: Code lua in a table

[Jeong Dal <haksan@me.com>]

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.hagen@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
> -----------------------------------------------------------------

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