Re: Releasing several Holds simultaneously
- To: mathgroup at smc.vnet.net
- Subject: [mg82268] Re: Releasing several Holds simultaneously
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Wed, 17 Oct 2007 03:44:45 -0400 (EDT)
- References: <ff1po5$90n$1@smc.vnet.net>
Andrew Moylan wrote:
> Hold[a := Hold[1]]
>
> How can I release both of these Holds (and thus execute a:=1)
> simultaneously?
>
> ReleaseHold[%] doesn't work; it evaluates a := Hold[1] before the other hold
> is removed.
>
Hi Andrew,
How did you construct the expression Hold[a := Hold[1]]? Perhaps there
is a way to avoid the double Hold and construct Hold[a := 1] directly
(even if there is an expression in place of '1' that must not be
evaluated), using Unevaluated[].
> % /. Hold[x_]:>x does the same thing, because /. only matches once per part.
>
If you use Replace instead of ReplaceAll, then you can specify the level
at which the replacement should be done.
Replace[Hold[a := Hold[1]], Hold[x_] -> x, {2}]
--
Szabolcs