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Re: Bug in Pattern Matching with Condition?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97344] Re: Bug in Pattern Matching with Condition?
  • From: Raffy <raffy at mac.com>
  • Date: Wed, 11 Mar 2009 04:25:03 -0500 (EST)
  • References: <goqpe7$lrn$1@smc.vnet.net> <goqugt$ngp$1@smc.vnet.net>

On Mar 10, 3:32 am, dh <d... at metrohm.com> wrote:
> Hi Jens,
>
> can you elaborate a bit. According to the definition of Verbatim ,
>
> Verbatim[Condition][_, _]] should match literally "Condition][_, _]" and
>
> not Condition[a, b]. Therefore it looks more like  another bug to me an=
d
>
> adds to the mystery of why MatchQ[Condition[a, b], Condition[_, _]]
>
> evaluates to False.
>
> Daniel
>
>
>
> Jens-Peer Kuska wrote:
> > Hi,
>
> > but
>
> > MatchQ[Condition[a, b], Verbatim[Condition][_, _]]
>
> > Regards
> >    Jens
>
> > cesar wrote:
> >> Hi Mathematica group, do you get any idea of
> >> why the following sentences don't give true?
>
> >> MatchQ[Condition[a, b], Condition[_,_]]
> >> MatchQ[Condition[a, b], Condition[__]]
> >> MatchQ[Condition[a, b], HoldPattern[Condition[__]]]
>
> >> Is this a bug?
>
> >> Cheers,
> >> Cesar

As I said above, as a pattern, Condition[_,_] cannot match anything by
definition.  Since, Condition[_,_] => _ /; _ where the second _ must
evaluate to true for the rule to be accepted.  Since _ is obviously
not true, the rule can never be true.

If you want to use pattern matching to match Condition, I'd recommend
swapping its head with something else.


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