Re: Weird localization bug!
- To: mathgroup at smc.vnet.net
- Subject: [mg106044] Re: Weird localization bug!
- From: dh <dh at metrohm.com>
- Date: Thu, 31 Dec 2009 03:15:23 -0500 (EST)
- References: <hhf5pa$h0e$1@smc.vnet.net>
Hi,
according to the manual, Rule should evaluate its arguments normally
(with the exception of Sequence). Now consider:
makerule[input_] := Rule[(input /. a_Integer :> 2 a), input];
Trace@makerule[5]
You will see that the first a is localized, the second not. There
seems to be a problem with nested rules. I would report this to
Wolfram.
Daniel
On 30 Dez., 10:16, Derek Yates <yat... at mac.com> wrote:
> I can't figure this out, and think it is a bug. I'm using Mathematica
> 7.0.0 and get the same behaviour on both Mac OS X (10.5.8) and on
> Windows XP.
>
> I want a function which creates a rule. The rule is of the form
> "manipulated input" -> "input". Here is my first attempt (I have
> simplified from what I really want to do, in order to illustrate the
> bug):
>
> (1) makerule[input_] :=(input /. a_Integer :> 2 a) -> input
> In: makerule[5]
> Out: 2a->5
>
> (I expect to get 10->5)
>
> (2) makerule2[input_] := (input /. a_Integer :> 2 a)~myrule~input
> In: makerule2[5]
> Out: myrule[10,5]
>
> as expected
>
> Forcing an extra layer of localization seems to squash the bug:
>
> (3) makerule3[input_] :=Block[{inputcopy = input},(input /.
> a_Integer :> 2 a) -> inputcopy]
> In: makerule[5]
> Out: 10->5
>
> Is it a bug, or have I misunderstood how the localization is meant to
> work?