Re: ValueList command
- To: mathgroup@smc.vnet.net
- Subject: [mg10527] Re: ValueList command
- From: daiyanh@interramp.com (Daitaro Hagihara)
- Date: Tue, 20 Jan 1998 02:23:14 -0500
- Organization: Self-Organization
- References: <34BE8A1E.11C8139B@mediaone.net>
In article <34BE8A1E.11C8139B@mediaone.net>, Hitoshi Yamamoto
<hitoshi@mediaone.net> wrote:
>When I upgraded Mathematica to 3.0, one package (called HIP) stopped
>working. I traced it down to a command used in the package 'ValueList'.
>Unfortunately I don't have the old verion of mathamatica and cannot
>check the package with it. Does anybody know what 'ValueList' does? It
>is not found in the Mathematica book.
>
>Thanks in advance for the assistance.
>
>- Hitoshi Yamamoto
>
>
This ValueList, which I presume to be unavailable on v.3 of Mathematica,
is essentially the same command as HoldForm, except that InputForm as
well as OutputForm of the output from ValueList is the same unevaluated
form of the input itself, without ValueList head, since ValueList has
the HoldAll attribute set. Normally you cannot achive this effect
using the ordinary built-in commands. ValueList is non-ordinary in
that its online documentation simply defines it as an internal symbol,
and it is not even discussed in Wolfram's book. It is, however,
different from hypothetical HoldTemporary in that the output expression
still has the ValueList head as evidenced from FullForm expression.
Thus the next evaluation of the output from ValueList evaluates to the
same unevaluated form of the original input, just like HoldForm. Come
to think of it, this ValueList is probably better than HoldTemporary
for certain applications. And for that, I thank you for "introducing"
this esoteric command. I don't know if there is a wrap remover
equivalent of ReleaseHold. To give you some concrete examples, take a
look at below:
Mathematica[4]? ValueList[Plus[1,2^2,3]]
2
1 + 2 + 3
Mathematica[5]? Out[4]
2
1 + 2 + 3
Mathematica[6]? Out[4]//InputForm
1 + 2^2 + 3
Mathematica[7]? Out[4]//FullForm
ValueList[Plus[1, Power[2, 2], 3]]
I hope this helps. BTW, you can use your old Mathematica 2.2 FrontEnd
with new Mathematica 3.0 Kernel, and you can switch back to 2.2 Kernel
thru Kernels and Tasks menu item under Action menu. A friend of mine
uses this technique to use both v.2.2 and v.3.0 kernels, saying that
some old (but still useful) packages are not yet updated to the new
standards of v.3. Unless you built the original package yourself,
trying to modify it may be hazardous to the health of both Mathematica
and you. And that is definitely beyond the scope of Wolfram's teck
support.