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

MathGroup Archive 2008

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

Search the Archive

Re: Scoping question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85744] Re: [mg85677] Scoping question
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Wed, 20 Feb 2008 07:06:41 -0500 (EST)
  • References: <200802190654.BAA27575@smc.vnet.net>

On Feb 19, 2008, at 1:54 AM, Yaroslav Bulatov wrote:

> The code below defines a function with parameter x. The body contains
> another function definition which uses this parameter. Why do "inner x
> is" and "outer x is" lines start reporting different values at one
> point?
>
> f1[x_] := (
>   f2[y_] := (Print["inner x is ", x]; If[x + 1 < 3, f1[x + 1], 1]);
>   (Print["outer x is ", x]; f2[#]) & /@ Range[2];
>   )
> f1[1

Because f2 is a global symbol and when f1[2] is executed it redefines  
f2, including the value x refers to.  You shouldn't use () as a  
scoping construct, strictly speaking it isn't a scoping construct, it  
overrides evaluation order but not scope.  Define f2 locally with  
Module and then your function will run as I believe you want it to.

f1[x_] :=
  Module[{f2},
   f2[y_] := Block[{}, Print["inner x is ", x]; If[x + 1 < 3, f1[x +  
1], 1]];
   Block[{}, Print["outer x is ", x]; f2[#]] & /@ Range[2]; ]

Regards,

Ssezi


  • Prev by Date: Re: Localizing Large Numbers of Variables in a DynamicModule:
  • Next by Date: Re: Plotting points of the function at increments.
  • Previous by thread: Scoping question
  • Next by thread: Re: Scoping question