TeX macro to merge two lists, bit like Python's zip

TeX macro to merge two lists, bit like Python's zip

[luigi scarso]

J. Fine asked sometime ago something like python's zip tha merge two
"lists" element by element, cfr.
http://groups.google.com/group/comp.text.tex/browse_thread/thread/2c1feea4ad19501e/cf6f849c5b81e76c?show_docid=cf6f849c5b81e76c

Here is the idea: a list is zero or more control sequence, ie
{} is an empty list,
\Alpha\Beta
is a list with 2 elements, and so on.
\zip{\Alpha\Beta}{\Gamma\Delta} gives \Alpha\Gamma\Beta\Delta


\starttext
% Hans's hint
% \def\zipthem#1#2%
%  {\def\dozipthem##1{\def\dodozipthem####1{1\string##1
2\string####1}\handletokens#2\with\dodozipthem}%
%   \handletokens#1\with\dozipthem}

 \def\myzipthem#1#2%
  {\ctxlua{A = {}; B = {}}
   \def\dozipthemA##1{\ctxlua{table.insert(A,[[\string##1]])}}%
   \def\dozipthemB##1{\ctxlua{table.insert(B,[[\string##1]])}}%
   \handletokens#1\with\dozipthemA
   \handletokens#2\with\dozipthemB%
   \ctxlua{%
      for i=1,math.max(table.maxn(A),table.maxn(B)) do
       local a = ""
       local b = ""
       if A[i] then a = '\\string' ..A[i] end
       if B[i] then b = '\\string' ..B[i] end
       tex.sprint(a,b)
      end
      tex.print([[\blank]])
      for i=1,math.max(table.maxn(A),table.maxn(B)) do
       local a = A[i] or ""
       local b = B[i] or ""
       tex.sprint(a,b)
      end
      tex.print([[\blank]])
   }
  }
\def\Alpha{A}
\def\Beta{B}
\def\Gamma{C}
\def\Delta{D}
\myzipthem{\Alpha\Beta}{\Gamma\Delta}%gives \Alpha\Gamma\Beta\Delta
\myzipthem{}{\Gamma\Delta}
\stoptext

For ours bloggers.

-- 
luigi
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