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Re: evaluate to True?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125928] Re: evaluate to True?
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Sat, 7 Apr 2012 05:58:44 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201204061001.GAA23045@smc.vnet.net>

You mean MemberQ rather than ModuleQ.  In MemberQ[list, expr_] a blank
(with or without a name for the blank) matches anything.

{MemberQ[{a}, _],
 MemberQ[{"a"}, _],
 MemberQ[{Indeterminate}, _],
 MemberQ[{ComplexInfinity}, _],
 MemberQ[{Plot[x, {x, 0, 1}]}, _]}

{True, True, True, True, True}


Bob Hanlon

On Fri, Apr 6, 2012 at 6:01 AM, Christoph Lhotka
<christoph.lhotka at fundp.ac.be> wrote:
> Hello,
>
> I found and interesting subject of discussion in the post
>
> "Bug in pattern test, or I did something wrong?"
>
>
> I could trace back the problem to an issue with ModuleQ.
>
> Question: Why does
>
> In[12]:= ModuleQ[{0,1,2},expr_]
>
> Out[12]:= True
>
> evaluate to True?
>
>
> My argumentation is as follows:
>
> On the one hand there could be a chance that expr_ is 0,1 or 2 but on
> the other
> hand the probability that expr_ is not 0,1 or 2 is even higher. As a
> conclusion it should neither
> evaluate to True nor to False.
>
> In other words: Is there any reason why the expression of everything
> (named expr)
> is contained in the set {0,1,2} ?
>
> Best,
>
> Christoph
>



-- 
Bob Hanlon



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