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Re: Fine control of evaluation

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  • Subject: [mg126459] Re: Fine control of evaluation
  • From: Bob Hanlon <hanlonr357 at>
  • Date: Sat, 12 May 2012 04:53:29 -0400 (EDT)
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  • References: <>

step1 /. func1 -> f


step1 /. HoldPattern[func1[x_]] -> func1[x]

However, the first approach won't work correctly in more general cases such as when

func1[x_] := f[7x-2]

Bob Hanlon

Sent from my iPhone

On May 11, 2012, at 12:13 AM, Brentt <brenttnewman at> wrote:

> Hello, I am struggling with evaluation control and was hoping someone might
> point me in the right direction. I vaguely remember seeing something in the
> manual or the tutorials addressing this issue, but I can't find the section
> I saw it in.
> How does one get fine control over things wrapped in Hold and HoldForm. Say
> I have some functions
> func1[x_]:= f[x];
> func2[x_] := g[x];
> step1 = HoldForm[ func1[x]+ func2[x] ];
> Now say I want the statements wrapped in HoldForm,  func1[x]+ func2[x]  to
> evaluate to f[x]+ func2[x]
> I thought naturally it would be something like
> step2 = HoldForm[ Evaluate[func1[x]]+ func2[x] ] ;
> But then HoldForm seems a bit overzealous about it's task, and outputs
> Evaluate[func1[x]]+ func2[x]---it leaves Evaluate unevaluated.  (I tried
> wrapping it func1[x] in ReleaseHold to no avail.)
> The above is just pseudocode, Maybe there is some specifics about what I
> was actually doing that was causing the unintuitive behavior (i.e. HoldForm
> holding Evaluate, instead of, well, evaluating.) What I was doing was more
> along these lines:
> ----------------
> ubounds= {u,0, pi};
> vbounds={v,0,2pi};
> t[dir_]:= D[s[u,v],dir_];    (*where dir_ is going to be either u or v*)
> (*here is the difficult part:*)
> formattedOutput= Integrate[HoldForm[t[u]] , ubounds, vbounds ]
> //TraditionalForm;
> ----------------
> The issue is that I want the t[u] wrapped in the HoldForm to evaluate to
> D[s[u,v],dir_], and hold that. If I wrap it in Evaluate, HoldForm holds
> Evaluate (puzzling), and tries to integrate Evaluate as if it is the
> integrand. I've tried all kinds of permutations of HoldForm, Defer,
> ReleaseHold, Evaluate, and I haven't had anything to work.
> Thank you for any help or pointing me in the right direction

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