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MathGroup Archive 1999

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Re: ReplaceAll in If Statement

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19462] Re: [mg19448] ReplaceAll in If Statement
  • From: "Andrzej Kozlowski" <andrzej at tuins.ac.jp>
  • Date: Sat, 28 Aug 1999 15:52:58 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

The problem is very simple. {True} is not the same as True. Change your 
definition  od test to

test[opts___] := Module[{},
If[a /. opts, z = 1, z = 2, z = 3]; {a, z} /. opts]

and you will get the behaviour you expected:

In[10]:=
test[opList]
Out[10]=
{True, 1}

--
Andrzej Kozlowski
Toyama International University
JAPAN
http://sigma.tuins.ac.jp
http://eri2.tuins.ac.jp


----------
>From: "Tom Compton" <comptont at concentric.net>
To: mathgroup at smc.vnet.net
>To: mathgroup at smc.vnet.net
>Subject: [mg19462] [mg19448] ReplaceAll in If Statement
>Date: Wed, Aug 25, 1999, 6:25 AM
>

> In the following sequence I expected z to evaluate to 1 in the
> Module.  It appears that the test in the module does not
> evaluate to either True or False.  I don't understand why.
> Can anyone explain?
>
> In[1]:=
> opList={a->True};
>
> In[2]:=
> test[opts___]:=Module[{},
> If[a /. {opts}, z=1, z=2, z=3];
> {a, z} /. {opts}]
>
> In[3]:=
> test[opList]
> Out[3]=
> {{True,3}}
>
>
>
> Tom Compton
>
>
>
> 


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