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Re: Null Return for a Module

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88690] Re: Null Return for a Module
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Mon, 12 May 2008 06:57:00 -0400 (EDT)
  • References: <g0903j$kpp$1@smc.vnet.net>

Hi,

try

Test[] := Module[{i, thesum}, thesum = 0;
   For[i = 1, i <= 3, i++, thesum = thesum + i]; (* <= Here *)
   Return[thesum]]

For[] return Null and since you have forgotten the CompoundExpression[] ";"

the result is interpreted as a product For[__]*Return[_]
and since Return[] does not work in expressions, you
get Null*Return[6]

Regards
   Jens


Dave the Funkatron wrote:
> Hi all,
> 
> I'm getting strange output and am trying to track down what might be
> causing it. I have the following code in my .nb file:
> 
> (* begin code *)
> 
> Test[ ] := Module[ {i, thesum},
>   	thesum = 0;
>   	For[ i = 1, i <= 3, i++,
>     		thesum = thesum + i
>     	]
>    	 Return[ thesum  ]
>   ]
> 
> Test[ ]
> 
> (* end code *)
> 
> 
> The output I would expect would be simply
> 
>   6
> 
> But, I get
> 
>   Null Return[6]
> 
> Alternatively, if I change the last line of the Test function to be
> 
>    	thesum
> 
> instead of
> 
>    	Return[ thesum ]
> 
> I get
> 
>   6 Null
> 
> as the output. If I remove the for loop, I get expected behavior,
> i.e.,
> 
> 
> Test[ ] := Module[ {i, thesum},
>   	thesum = 1 + 2 + 3;
>   	(*
>   	For[ i = 1, i <= 3, i++,
>   		thesum = thesum + i
>   	]
>   	*)
>   	 Return[ thesum  ]
>   ]
> 
> yields the output
> 
>   6
> 
> as one might expect. I'm not sure what this all means, or what it is
> complaining about. I have other for-loops that are apparently working
> properly. So, can anyone give me an idea what might be going wrong
> here?
> 
> Thanks.
> 
> Dave
> 
> 
> 


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