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

Hans Hagen Mon, 20 Jul 2020 01:37:01 -0700

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 cando 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 gofurther, 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 expandedbecause that is what mp does (i'll probably cook something for that someday).


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



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                                          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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