Re: HoldForm in defined function doesn't seem to work
- To: mathgroup at smc.vnet.net
- Subject: [mg99248] Re: [mg99182] HoldForm in defined function doesn't seem to work
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Fri, 1 May 2009 05:19:44 -0400 (EDT)
- Reply-to: hanlonr at cox.net
The function needs to have the attribute HoldAll or HoldFirst
f[x_] = HoldForm[x];
SetAttributes[g, HoldAll]
g[x_] = HoldForm[x];
f[113 456 789]
40655592
g[113 456 789]
113 456 789
Attributes[HoldForm]
{HoldAll,Protected}
Bob Hanlon
---- joel.aufgang at gmail.com wrote:
=============
I'm struggling to understand why this doesn't work:
f[x_] = HoldForm[x];
HoldForm[123 456 789] (* returns "123 x 456 x 789" *)
f[123 456 789] (* returns"44253432" *)
I don't understand why the two results are different. Is there a
special trick I need to do to be able to define f so that the HoldForm
works?
I'm using this to help visualize the way a notebook represents typed
expressions, so I'm trying to do something like this:
BoxTree[expr_] := TreeForm[ToBoxes[HoldForm[expr]][[1]]];
a b c d e // BoxTree
123 456 789 // BoxTree (* want this to show as a RowBox like the
previous example *)
Any help would be greatly appreciated. Thanks.