Using Lua functions with mplib and mpgraph

Question

This question has reference to the question Error with Lua, Luamplib and Mpgraph I am trying to use lua functions inside mplib. The detailed code is here.

\documentclass{article}
\usepackage{luacode}
\usepackage{luamplib}
\begin{document}
\begin{luacode}
  require("math")
   local sin=math.sin;
\end{luacode}
\def\plot{%
  \directlua{
luamplib.process_mplibcode([[
    input graph ;
    beginfig(0)
    draw begingraph(5cm,3cm)
       gdraw (0,sin(0)) for x = 1 upto 3: .. (x, sin(x)) endfor ;
    endgraph ;
    endfig ;
  ]])}%
}
\plot
\end{document}

There seems some problem with intermingling of lua and mplib. Where would be the problem and how can this be corrected?

Answer 1

You can access Lua from within mplib using the runscript function.

\documentclass{article}
\usepackage{luamplib}
\begin{document}
\def\plot{%
  \directlua{luamplib.process_mplibcode([[
    vardef sin primary x =
        runscript("mp.print(math.sin(" & decimal x & "))")
    enddef ;
    input graph ;
    beginfig(0)
    draw begingraph(5cm,3cm)
       gdraw (0,sin(0)) for x = 1 upto 3: .. (x, sin(x)) endfor ;
    endgraph ;
    endfig ;
  ]])}%
}
\plot
\end{document}