Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: pass by reference

  • To: mathgroup at smc.vnet.net
  • Subject: [mg93724] Re: pass by reference
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Mon, 24 Nov 2008 04:12:39 -0500 (EST)
  • Organization: University of Bergen
  • References: <gg8p9s$jsp$1@smc.vnet.net>

juan flores wrote:
> Dear all,
> 
> How do you pass by reference in Mathematica?

You don't.  Mathematica doesn't work that way.

> 
> Let us say we want to program push and pop.
> --------
> Push[el_, stack_] := Prepend[stack, el]
> Pop[stack_] := {First[stack], Rest[stack]}
> 
> stack = {1, 2, 3}; newel = 5;
> 
> stack = Push[newel, stack]
> {5, 1, 2, 3}
> 
> {lastel, stack} = Pop[stack]
> {5, {1, 2, 3}}
> 
> stack
> {1, 2, 3}
> --------
> 
> Code is working, but it is kind of awkward to have to use pure
> functional programming.  I have not been able to find the way to pass
> parameters by reference (or name - i.e. macros).
> 
> Any pointers/ideas will be greatly appreciated.
> 

My advice is: don't force a programming style on Mathematica that 
doesn't fit it.  This is just going to cause you a lot of frustration.

I can't provide alternatives, though, since you did not say what is the 
real problem that you're trying to solve (instead you made up an 
artificial programming problem).

ClearAll[push, pop]

SetAttributes[push, HoldRest]
push[el_, stack_] := PrependTo[stack, el]

SetAttributes[pop, HoldAll]
pop[stack_] := With[{el = First[stack]},
   stack = Rest[stack];
   el]


  • Prev by Date: Re: pass by reference
  • Next by Date: Re: FFT in Mathematica
  • Previous by thread: Re: pass by reference
  • Next by thread: Re: pass by reference