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

29 May 2020

      On 5/28/2020 11:24 PM, context@vivaldi.net wrote:
...
Hello,
one more question - why macros \Undefined and \DoNothing show "defined" 
although I (tried to) undefine them?
----
\starttext
   \def\MyMacro{Ahoj}
   \def\MyMac#1#2{Something}
  \def\Undefined{}
   \let\Undefined\undefined
  \def\DoNothing{}
   \let\DoNothing\donothing
  \startluacode
     local str = { [true] = "defined", [false] = "undefined" }
    local function whatever(s)
       context.type("\\" .. s)
       context(" is " .. (tokens.defined(s) and "defined" or 
"undefined")) --% Hans' way
       context(" and is " .. str[token.is_defined(s)] .. ".") --% 
Henri's way
       context.par()
     end
    whatever("MyMacro")
     whatever("MyMacroD")
     whatever(" ")
     whatever("-")
     whatever("Undefined")
     whatever("DoNothing")
   \stopluacode
  %\Undefined % Causes "! Undefined control sequence"
\stoptext
----
Gives:
"
\MyMacro is defined and is defined.
\MyMacroD is undefined and is undefined.
\ is defined and is defined.
\- is defined and is defined.
\Undefined is defined and is defined.
\DoNothing is defined and is defined.
"
Because the macro actually *is* defined: as soon as tex sees
\foo

it reserves the name and gives it the meaning undefined, so even 
\undefined is defined.

Anyway, that is why we have \ifdefined that does a different kind of 
checking. In retrospect, that is a better one, so I'll adapt that in lmtx.

\starttext
   \let\MyMacroA\undefined

   \startluacode
     local function whatever(s)
         context.type("\\" .. s)
         context(" is " .. (tokens.defined(s,true) and "defined" or 
"undefined")) --% Hans' way
         context(" and has meaning " .. (tokens.defined(s) and "defined" 
or "undefined")) --% Hans' way
         context.par()
     end

     whatever("MyMacroA")
     whatever("MyMacroB")
   \stopluacode

\stoptext

\MyMacroA is defined and has meaning undefined
\MyMacroB is undefined and has meaning undefined

You can do this in current luatex/mkiv:

     if CONTEXTLMTXMODE == 0 then

         local d = tokens.defined
         local c = tokens.create

         function tokens.defined(s,b)
             if b then
                 return d(s)
             else
                 return c(s).cmd_name == "undefined_cmd"
             end
         end

     end

Hans

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                                           Hans Hagen | PRAGMA ADE
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