Re: Weird localization bug!
- To: mathgroup at smc.vnet.net
- Subject: [mg106070] Re: [mg106009] Weird localization bug!
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Thu, 31 Dec 2009 03:20:21 -0500 (EST)
- Reply-to: hanlonr at cox.net
Perhaps one of these is what you want
Clear[makerule]
makerule[input_Integer] :=
2*input -> input
makerule /@ {5, 5 x}
{10->5,makerule(5 x)}
Clear[makerule]
makerule[input_] :=
input /. a_Integer :> (2 a -> a)
makerule /@ {5, 5 x}
{10->5,x (10->5)}
Bob Hanlon
---- Derek Yates <yatesd 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?