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MathGroup Archive 2006

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Re: "short circuiting" And and Or

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70624] Re: "short circuiting" And and Or
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Sat, 21 Oct 2006 05:14:21 -0400 (EDT)
  • References: <eha5b7$b5b$1@smc.vnet.net>

Szabolcs Horvat wrote:
> I'd like to write a function that tests whether there are any elements
> in a list that violate a certain condition. I could simply use
> And@@condition/@list, but for reasons of efficiency I'd like to stop
> the testing as soon as a "False" value is found. Is there any elegant
> way of doing this without writing an explicit While loop?
> 
> Szabolcs Horvát
> 
Hello,

The following program illustrates that this is already the behaviour:

f1[]:=(Print["f1"];False);
f2[]:=(Print["f2"];False);

f1[] && f2[]

Notice that And has attribute HoldAll - so it can evaluate its arguments 
as required, and that it does not have attribute Orderless - so the 
arguments can't get permuted.

David Bailey
http://www.dbaileyconsultancy.co.uk






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