\show for Lua commands

Question

TeX (and all newer engines) has the primitive \show which helps me probe macros, and most of the time is enough to understand/remember the implementation (rather than having to go back to the source code).

Is there something similar for Lua commands? For instance, Heiko Oberdiek has written replacements for some pdfTeX primitives in LuaTeX, and I'd like to get more information about them using some hypothetical \showluatexcmd macro.

\input pdftexcmds.sty
\catcode`@=11
\show\pdf@strcmp
%\showluatexcmd{oberdiek.pdftexcmds.strcmp}
\bye

Answer 1

I seriously doubt that there is something similar for Lua, but you can do the following to find out where the function is defined (to get to the source code).

\directlua{ require("showluatexcmd") }
\def\showluatexcmd#1{\directlua{showluatexcmd.show(#1)}}

\input pdftexcmds.sty
\catcode`@=11
 \show\pdf@strcmp
\showluatexcmd{oberdiek.pdftexcmds.strcmp}
\bye

and the file showluatexcmd.lua:

module(...,package.seeall)

function show( fun )
  local debuginfo = { "source","linedefined","what" }
  for _,v in ipairs(debuginfo) do
    texio.write_nl(string.format("%20s=%q", v, debug.getinfo(fun)[v]))
  end
end

One could extend this probably to directly load the function and display it. But in most cases this won't help as there are a lot of functions that are short and call other functions.

A sample output is

          source="@/opt/texlive2011/texmf-dist/scripts/oberdiek/pdftexcmds.lua"
     linedefined="46"
            what="Lua" )