Dear Hans,

Your code works fine.

> \starttext
> 
> \startMPcode
>    numeric maxCount;
>    maxCount := 10;
>    setglobalmacro("MyMacro",decial maxCount);
>    setglobalcount("MyCount",maxCount);
> \stopMPcode
> 
> 
> \dorecurse{\MyMacro}{It is \recurselevel. }\par
> \dorecurse{\MyCount}{It is \recurselevel. }\par
> 
> \stoptext

I applied your method to my code as following. 

\newcount\udCount  %%% add count
\startMPinitializations%{UDBasic}
  pair A,B,C,D;
  pair E, F, G, H;
  path p,q;
  numeric ang,maxNum;

  numeric n; %AM Added

  u:=1in;
  A=(.95*TextWidth,u); B=(0,u); C=(0,0); D=(.95*TextWidth,0);
  p := A--B--C--D;
  q := (TextWidth,1.5u)--(0,1.5u)--(0,-.5u)--(TextWidth,-.5u)--cycle;
  z0=(.1u,0);
  
   vardef nextPt (expr M,N) = 
   if ypart(N) = 0: 
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[A,B];
   else:
       H := whatever[N, N + dir(.5*angle(M-N))*u] = whatever[C,D];
   fi;
   H
   enddef;

   def grayUD(expr i) =
      draw G -- if ypart(B)=ypart(G): B -- C else: C -- B fi --z[i];
      filldraw z[i]+2*(G-z[i])*u -- z[i] -- z[i+1] -- z[i+1]+(G-z[i])*u -- cycle withcolor .75white; 
      draw G -- z[i+1] dashed evenly;
      draw z[0] for k=0 upto i: --z[k] endfor dashed evenly;
      clip currentpicture to q;
   enddef;

   def linesUD(expr i) =
      draw p;
      draw z0 for k=0 upto i+1: --z[k] endfor dashed evenly;

      % AM: removed. Set in in the main code
      % setbounds currentpicture to boundingbox q;
   enddef;

   ang := 40;
   z[1] = whatever[z[0], z[0]+dir(ang)*u] = whatever[A,B];

   % AM: Changed next line from G to z[-1]
   z[-1] = whatever[z[0], z[0]+dir(2*ang)*u] = whatever[A,B];
   for k = 2 upto 20:
      z[k] = nextPt(z[k-2],z[k-1]);
      maxNum := k;
      exitif xpart(z[k]) > TextWidth;
   endfor;
   maxNum := maxNum-1;
   setglobalmacro("udMacro",decimal maxNum);  %%% define udMacro and udCount
   setglobalcount("udCount",maxNum);

\stopMPinitializations

\startuseMPgraphic{foldUD}{num}
   numeric n;
   n := \MPvar{num}-1;
   G := z[n-1];
   grayUD(n);
\stopuseMPgraphic
\startuseMPgraphic{dotLines}{num}
   numeric n;
   n := \MPvar{num}-1;
   linesUD(n);
\stopuseMPgraphic

\setupinteraction[state=start]
\usemodule[animation]
\starttext
%\startanimation[menu=yes]
%{
\dorecurse{\udCount}
 {\useMPgraphic{foldUD}{num=\recurselevel}}
 {\useMPgraphic{dotLines}{num=\recurselevel}}
%}
%\stopanimation
\stoptext

1. Using “udCount” doesn’t issue error message, but it draws the path p only.
2. Using “udMacro” issue the error message.

Is there anything that I miss?

Best regards,

Dalyoung

**********
tex error       > tex error on line 75 in file /Users/graph/Library/Mobile Documents/com~apple~CloudDocs/texMain/funmath/foldBandMPnew.tex: Undefined control sequence

<argument> \udMacro 
    
<macro> \dorecurse #1->\ifcase #1
    \relax \expandafter \gobbletwoarguments \or \expandafter \syst_helpers_recurse_y \else \expandafter \syst_helpers_recurse_x \fi {#1}
<line 3.75> \dorecurse{\udMacro}
    
65        numeric n;
66        n := \MPvar{num}-1;
67        linesUD(n);
68     \stopuseMPgraphic
69     
70     \setupinteraction[state=start]
71     \usemodule[animation]
72     \starttext
73     %\startanimation[menu=yes]
74     %{
75 >>  \dorecurse{\udMacro}
76      {\useMPgraphic{foldUD}{num=\recurselevel}}
77      {\useMPgraphic{dotLines}{num=\recurselevel}}
78     %}