Re: delayed rule evaluation order
- To: mathgroup at smc.vnet.net
- Subject: [mg68016] Re: [mg67967] delayed rule evaluation order
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Thu, 20 Jul 2006 06:04:56 -0400 (EDT)
- References: <11710934.1153306359682.JavaMail.root@eastrmwml07.mgt.cox.net> <acbec1a40607190514x62d0f07byeb91cf8b496bca33@mail.gmail.com> <3BA57237-C0B6-4C71-A8B0-3481DCDBC464@mimuw.edu.pl> <acbec1a40607190919p3efa8b30x4ae0cb6278444931@mail.gmail.com>
- Sender: owner-wri-mathgroup at wolfram.com
It's much easier to answer questions if the persons who pose them
explain clearly what they mean.
The most obvious way to modify my code seems to me to be:
f[1] = 1;
f[n_Integer] /; n > 1 = n f[n - 1];
InputForm[z = Trace[f[2]]];
Block[{f=g},z/.{HoldForm[a_]:>HoldForm@@{SetPrecision[a,3]}}]/.g->f
{f(2.00),{True,True},2.00 f(1.00),{{1.00,1.00},f(1.00),1.00},2.00,2.00}
Now f is not evaluated. The only thing you might still complain about
is that {2 > 1, True} evaluated to {True,True}. If you really care
about this you, can prevent it in various ways, for example:
Block[{f=g},
z/.{HoldForm[a_]/;
FreeQ[a,True]:>HoldForm@@{SetPrecision[a,3]}}]/.g->f
{f(2.00),{2>1,True},2.00 f(1.00),{{1.00,1.00},f(1.00),1.00},2.00,2.00}
or
Block[{f=g,Greater=greater},
z/.{HoldForm[a_]/;
FreeQ[a,True]:>HoldForm@@{SetPrecision[a,3]}}]/.{g->f,greater-
>Greater}
{f(2.00),{2.00>1.00,True},2.00 f(1.00),{{1.00,1.00},f(1.00),1.00},
2.00,2.00}
There are many other possibilities.
If there is still anything you do not like than it probably means you
still have not explained completely what you want.
Andrzej Kozlowski
On 19 Jul 2006, at 18:19, Chris Chiasson wrote:
>
> What I want it to do is be able to replace numbers that aren't direct
> arguments of HoldForm (maybe they are nested a few levels deep, etc).
>
> In the example you sent me, f is evaluated - which is undesirable
> for me.
>
> On 7/19/06, Andrzej Kozlowski <akoz at mimuw.edu.pl> wrote:
>> (tm) Pro*
>> It seems to me that a variant of my first suggestion works fine:
>>
>> In[1]:=
>> f[1]=1;
>> f[n_Integer]/;n>1=n f[n-1];
>> InputForm[z=Trace[f[2]]];
>> InputForm[z/.{HoldForm[a_]:>HoldForm@@{SetPrecision[a,3]}}]
>>
>> Out[4]//InputForm=
>> {HoldForm[2.`2.9999999999999973],
>> {HoldForm[True], HoldForm[True]},
>> HoldForm[2.`2.9999999999999973],
>> {{HoldForm[1.`2.9999999999999973],
>> HoldForm[1.`2.9999999999999973]},
>> HoldForm[1.`2.9999999999999973],
>> HoldForm[1.`2.9999999999999973]},
>> HoldForm[2.`2.9999999999999973],
>> HoldForm[2.`2.9999999999999973]}
>>
>> Or is this not what you wanted?
>>
>> Andrzej Kozlowski
>>
>>
>>
>> On 19 Jul 2006, at 14:14, Chris Chiasson wrote:
>>
>> > Thanks to Kozlowski's, Hanlon's and Pein's solutions (haven't
>> received
>> > any others so far), I am now using this type of replacement:
>> >
>> > Hold[5.55555555]/.{blah_?InexactNumberQ:>
>> > junk[SetPrecision[blah,3]]}/.junk->Evaluate
>> >
>> > Hold[5.56]
>> >
>> > However, this still does not totally work on Trace's output:
>> >
>> > In[1]:=
>> > f[1]=1;
>> > f[n_Integer]/;n>1=n f[n-1];
>> > InputForm[z=Trace[f[2]]]
>> >
>> > Out[3]//InputForm=
>> > {HoldForm[f[2]], {HoldForm[2 > 1], HoldForm[True]}, HoldForm[2*f[-1
>> > + 2]],
>> > {{HoldForm[-1 + 2], HoldForm[1]}, HoldForm[f[1]], HoldForm[1]},
>> > HoldForm[2*1], HoldForm[2]}
>> >
>> > In[4]:=
>> > InputForm[z/.{blah_?ExactNumberQ:>junk[SetPrecision[blah,
>> 3]]}/.junk-
>> > >Evaluate]
>> >
>> > Out[4]//InputForm=
>> > {HoldForm[2.`2.9999999999999996], {HoldForm[Evaluate[SetPrecision
>> [2,
>> > 3]] > Evaluate[SetPrecision[1, 3]]],
>> > HoldForm[True]}, HoldForm[2.`2.9999999999999996],
>> > {{HoldForm[1.`2.9999999999999996], HoldForm
>> [1.`2.9999999999999996]},
>> > HoldForm[1.`2.9999999999999996],
>> > HoldForm[1.`2.9999999999999996]}, HoldForm[2.`2.9999999999999996],
>> > HoldForm[2.`2.9999999999999996]}
>> >
>> > Notice the leftover Evaluate and SetPrecision commands. Does anyone
>> > have ideas on how to get this to work?
>> >
>> > On 7/19/06, Bob Hanlon <hanlonr at cox.net> wrote:
>> >> Hold[{2, 3}] /.
>> >> {Hold[{x_, y_}] :> Hold[Evaluate[x^y]]}
>> >>
>> >> Hold[8]
>> >>
>> >>
>> >> Bob Hanlon
>> >>
>> >> ---- Chris Chiasson <chris at chiasson.name> wrote:
>> >> > Hold[{2, 3}] /. {{x_, y_} :> x^y}
>> >> >
>> >> > the result is Hold[Power[2,3]]
>> >> >
>> >> > I would like the result to be Hold[8]
>> >> >
>> >> > The original context is post-processing of a large Trace output
>> >> (via
>> >> > SetPrecision to get rid of digits and improve readability).
>> >> >
>> >> > Any ideas?
>> >> >
>> >> > --
>> >> > http://chris.chiasson.name/
>> >> >
>> >>
>> >> --
>> >>
>> >> Bob Hanlon
>> >> hanlonr at cox.net
>> >>
>> >>
>> >>
>> >
>> >
>> > --
>> > http://chris.chiasson.name/
>>
>>
>
>
> --
> http://chris.chiasson.name/