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MathGroup Archive 1995

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Re: Module/Block problem (passing pointers?)

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1854] Re: Module/Block problem (passing pointers?)
  • From: maeder at inf.ethz.ch (Roman Maeder)
  • Date: Mon, 7 Aug 1995 20:27:37 -0400
  • Organization: Theoretical Computer Science, ETH Zurich

> 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?

Not correct. The paradigm of in-out (or VAR, or reference) parameters
can be implemented like this (see "The Mathematica Programmer", APP, 1994,
Chapter 1):

SetAttributes[test2, HoldFirst]

test2[s_Symbol] := (
	s = True;
)


In[3]:= f = False;

In[4]:= test2[f]

In[5]:= f

Out[5]= True


Now you can do:

test1 := Module[{flag},
  Print["1,1 ",flag];
  test2[flag];
  Print["1,2 ",flag];
]

Roman Maeder


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