[NTG-context] Checking existence of a macro (control sequence) by Lua

[Hans Hagen]

On 5/28/2020 12:42 AM, context at vivaldi.net wrote:
> Hello,
> 
> is it possible to check whether a macro exists (or - is it a 
> non-\undefined control sequence) with Lua? Suppose:
> 
> ----
> \starttext
>    \def\MyMacro{Ahoj}
>    \def\MyMac#1#2{Something}
> 
>    \startluacode
>      IsDefined = function(ctl_seq)
>        print("CS " .. ctl_seq ..
>                                  (tex.IsCS(ctl_seq) -- Or what to come 
> here?
>                                                     "is defined" or "is 
> unknown") .. ".")
>      end
> 
>      -- So the function should print to the console:
> 
>      IsDefined("MyMacro") --> "CS MyMacro is defined."
>      IsDefined("MyMac") --> "CS MyMac is defined."
>      IsDefined("bf") --> "CS bf is defined."
>      IsDefined("dummy") --> "CS dummy is unknown."
> 
>    \stopluacode
> \stoptext
> ----
> 
> Is it possible?
A lot is possible. Take this:

            \def\MyMacroA{Ahoj A}
\unexpanded\def\MyMacroB{Ahoj B}
\frozen    \def\MyMacroC{Ahoj C} % in lmtx
          % \def\MyMacroC{Ahoj C} % barks

At the tex end you can check for several properties:

\ifusercmd \hbox     Y\else N\fi % in lmtx
\iffrozen  \hbox     Y\else N\fi % in lmtx
\ifusercmd \MyMacroA Y\else N\fi % in lmtx
\iffrozen  \MyMacroA Y\else N\fi % in lmtx
\iffrozen  \MyMacroC Y\else N\fi % in lmtx

At the Lua end you can check for being defined:

\startluacode
     local function whatever(s)
         context.type("\\" .. s)
         context(" is %s", tokens.defined(s) and "defined" or "undefined")
         context.par()
     end
     whatever("MyMacroA")
     whatever("MyMacroD")
     whatever(" ")
     whatever("-")
\stopluacode

alternatively you can say:

\startluacode
    local t = token.create("MyMacro")
    print(t.cmdname == "undefined_cs")
\stopluacode

which is less efficient unless you want to access more properties.

Hans

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