Re: Re: New version, new bugs
- To: mathgroup at smc.vnet.net
- Subject: [mg42945] Re: [mg42930] Re: New version, new bugs
- From: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>
- Date: Tue, 5 Aug 2003 02:04:58 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
The reason why you usage of HoldPattern[Plus] is nonsensical (as I
wrote in my original posting) is that Plus[a] evaluates to just a and
Plus[a,b] to Plus[a,b]. So if you evaluate
>> f[a] + f[b] + 1 /. HoldPattern[Plus][f[_] ..] :> 0 /; True
HoldPattern[Plus][f[_] ..] evaluates to f[_] .. and you do not get a
match. In you other cases you use HoldPattern[Plus] with more than one
argument, so things work differently. There is no mystery.
Your tone in this discussion has began to reasmble that of of someone
who tried and failed to get a job with Wolfram Reasearch or has some
other personal grudge so I propose to stop it all here.
Andrzej
On Monday, August 4, 2003, at 06:45 AM, Maxim wrote:
>
>
> Andrzej Kozlowski wrote:
>
>> Maxim has pointed out that RuleCondition has the attribute HoldFirst.
>> I
>> was too careless giving my explanation: what I meant to refer to was
>> the following difference between Condition and RuleCondition (which I
>> learned form Allan Hayes)
>>
>> Hold[a] /. a :> Condition[1 + 1,True]
>>
>> Hold[1+1]
>>
>> Hold[a] /. a :> RuleCondition[1 + 1, True]
>>
>> Hold[2]
>>
>>
>
> I have no idea what RuleCondition is for and how you can rewrite, say,
>
> 2/.x_:>x^2/;x>0
>
> using RuleCondition, but it's totally irrelevant; you say that
> something
> somewhere doesn't get evaluated -- then put Evaluate in the right
> place and
> demonstrate the difference. I have a feeling you won't succeed. And
> before
> you give yet another "conclusive demonstration", try also explaing how
> these
> four examples work:
>
> f[a] + f[b] + 1 /. HoldPattern[Plus][_, _] /; True :> 1
> f[a] + f[b] + 1 /. HoldPattern[Plus[_, _]] /; True :> 1
> f[a] + f[b] + 1 /. HoldPattern[Plus][_, _] :> 1 /; True
> f[a] + f[b] + 1 /. HoldPattern[Plus[_, _]] :> 1 /; True
>
> I'll try giving a suggestion why the four examples in my original
> posting
> (with f[_]..) work that way; it is probably related to the following:
>
> In[1]:=
> FreeQ[x+y+z,x+y]
> Cases[x+y+z,x+y,{0,-1}]
>
> Out[1]=
> False
>
> Out[2]=
> {}
>
> Even though Cases does pattern matching (the second argument can be a
> pattern), in this case it doesn't break the expression into
> Plus[Plus[x,y],z]
> (yes, I know that it is a documented feature). So my guess is that
> somewhere
> in the dark recesses of Mathematica pattern matcher this confusion
> between
> two approaches arises.
>
> Of course, maybe Jens-Peer Kuska will explain to me again how I don't
> know
> what I'm doing, but he did seem to be rather quiet lately...
>
> The real problem is that there isn't any complete specifications
> describing
> the behaviour of pattern matching. So it's not even possible to say if
> an
> example is correct/incorrect, one has to resort to simply pointing out
> inconsistencies...only it seems that developers sometimes have to
> resort to
> the same means.
>
> Exactly the same goes for the example with Module and variables
> renaming.
>
> Maxim Rytin
> m.r at prontomail.com
>
>
>
>
Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/
http://platon.c.u-tokyo.ac.jp/andrzej/