Re: Variable containing code
- To: mathgroup at smc.vnet.net
- Subject: [mg74971] Re: [mg74937] Variable containing code
- From: Carl Woll <carlw at wolfram.com>
- Date: Fri, 13 Apr 2007 02:02:21 -0400 (EDT)
- References: <200704120847.EAA24473@smc.vnet.net> <461E1AE2.10008@wolfram.com> <461E27E1.1020406@metrohm.ch>
Daniel Huber wrote:
> Hallo Carl,
> thank's a lot. I knew that there is some magic word around but I was
> not able to find it.
> However, this only solves half the problem. If I try:
> t1:=Print["Hello"];
> Set[ t2, Extract[OwnValues[t1],{1,2},Unevaluated] ];
> t2 does not evaluate the code, the reason is:
> Although OwnValues[t1] and OwnValues[t2] return similar results,
> Information (??) returns different results, namely: t1:=Print[Hello]
> and t2=Unevaluated[Print[Hello]]
> It looks like Set did not strip the "Unevaluated". Does Set not behave
> like a normal function?
Well, presumably you meant to use SetDelayed instead of Set. However, if
you replace Set (or SetDelayed) by foo, you get the same behavior:
In[6]:= foo[t2, Extract[OwnValues[t1], {1, 2}, Unevaluated]]
Out[6]= foo[t2, Unevaluated[Print["Hello"]]]
So, no functions strip the Unevaluated. There are many ways to get t2 to
have the same Information as t1, here are a couple:
OwnValues[t1] /. _HoldPattern->t2 /. RuleDelayed->SetDelayed
Function[rhs, t2:=rhs,HoldAll]@@Extract[OwnValues[t1],{1,2},Hold]
Carl Woll
Wolfram Research
> Daniel
>
> Carl Woll wrote:
>
>> dh wrote:
>>
>>> Hello,
>>>
>>> how can one get at the value of a variable if this value is executable
>>> code? E.g. consider variable t1:= Print["Hello"]. How can I set the
>>> value of a second variable t2 to the value of t1 without executing
>>> the code?
>>>
>>> Daniel
>>>
>>>
>>>
>>>
>> Try OwnValues[t1]
>>
>> Carl Woll
>> Wolfram Research
>>
>>
>
>
- References:
- Variable containing code
- From: dh <dh@metrohm.ch>
- Variable containing code