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Re: Why HoldForm[] shows this expression in red in notebook?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125076] Re: Why HoldForm[] shows this expression in red in notebook?
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Mon, 20 Feb 2012 02:52:39 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jhqml4$f9t$1@smc.vnet.net>

On 2/19/2012 1:32 PM, Nasser M. Abbasi wrote:
> foo[x_, v_] := Module[{z = v},
>     {x^z, Hold[x^z], HoldForm[x^z]}
>     ];

Hi Nasser,

I assume it is a warning that z (the Module variable) will not be evaluated.

One might expect foo[x,2] to give {..., HoldForm[x^2]}.  It will not 
because z never evaluates to 2 (the expression that was substituted for v)

Why this warning is not shown for Hold?  I don't know.  I guess the 
results from HoldForm might be more confusing because if how it is 
printed.  I fell into this trap with HoldForm before (when trying to use 
it in plot labels) but not with Hold (where I typically focus on the 
hold-properties rather than formatting).

So again, this is just a guess.

-- 
Szabolcs Horvát
Visit Mathematica.SE:  http://mathematica.stackexchange.com/



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