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RE: Sequence and Or

  • To: mathgroup at smc.vnet.net
  • Subject: [mg34196] RE: [mg34179] Sequence and Or
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Thu, 9 May 2002 05:15:57 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Thanks for the workaround!  It makes me wonder, though, why Or should
have the HoldAll attribute at all.

Bobby

-----Original Message-----
From: Andrzej Kozlowski [mailto:andrzej at platon.c.u-tokyo.ac.jp] 
To: mathgroup at smc.vnet.net
Subject: [mg34196] Re: [mg34179] Sequence and Or

Compare:

In[19]:=
Or[Sequence@@{True,False,True}]

Out[19]=
Sequence[True,False,True]

In[20]:=
Or[Evaluate[Sequence@@{True,False,True}]]

Out[20]=
True

In[21]:=
Or[Sequence[True,False,True]]

Out[21]=
True

The point is the HoldAll  attribute of Or. Because of it, when you enter

Or[Sequence@@{True,False,True}]  only a single argument is passed to Or 
but Or with a single argument returns:

In[22]:=
Or[x]

Out[22]=
x

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/



On Wednesday, May 8, 2002, at 02:57  PM, DrBob wrote:

> When I evaluate the following...
>
> {True,False,True}
> Or@@%
> Sequence@@%
> Or[%]
>
> the outputs are:
>
> {True,False,True}
> True
> Sequence[True,False,True]
> Sequence[True,False,True]
>
> while I had expected:
>
> {True,False,True}
> True
> Sequence[True,False,True]
> True
>
> What am I missing?
>
> Bobby Treat
>
>
>
>
>





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