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Module/Block problem (passing pointers?)

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  • Subject: [mg1847] Module/Block problem (passing pointers?)
  • From: sherod at boussinesq.Colorado.EDU (Scott Herod)
  • Date: Mon, 7 Aug 1995 20:26:23 -0400
  • Organization: University of Colorado at Boulder

I've got a problem that seems to call for using the Block construct over
a Module, but for other reasons, I Modules are more appropriate.  I'll
show the set-up with a Block and ask how I can make it a module.  Here
is the basic code.

test1 := Block[{flag},
  Print["1,1 ",flag];
  Print["1,2 ",flag];

test2 := Module[{},
  Print["2,1 ",flag];
  flag = True;
  Print["2,2 ", flag];

In[3]:= test1

1,1 flag
2,1 flag
2,2 True
1,2 True

This does what I want, ie "flag" is a local variable to the test1's
execution and test1 knows that the value of flag was set in test2.

I would really like test1 to be defined in terms of a Module, not a Block.
Any suggestions?

Oh, in the real problem, test2 is already a function and it would be
inelegant to have it return flag as well.

If it were possible to pass pointers it would be easy to send test2 the
flag pointer and then check it in test1.  But I believe that Mathematica
can only pass values, correct?

Scott Herod
Applied Mathematics
University of Colorado, Boulder
sherod at

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