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I am using the following two lines of code relatively frequently

f/:Plus[f[x_], f[y_], z___]:=f[x+y]+z
f/:Times[c_, f[x_]]:=f[c x]

and I was wondering if it is possible to automate the process.

What I have in mind, is to supply a list of heads to a function and the function will make definitions similar to those presented above, for every head in the list.

The idea is to have a package that defines a bunch of heads that behave like f above and exports them to the user without having to show the user how the behavior is implemented.

I'm interested in avoiding possible side-effects from the automation process, if there are any.

So, to sum up, is it possible to automate the two TagSetDelayed definitions presented above, in a package that safely exports the heads exhibiting the same behaviour as f, without major side-effects?

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1 Answer 1

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You mean something like:

Scan[
  Function[head,
    head /: Plus[head[x_], head[y_], z___] := head[x + y] + z;
    head /: Times[c_, head[x_]] := head[c x]
  ],
  {f, g, h}
]
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2
  • $\begingroup$ if it works in a package without any weird side effects, sure it does $\endgroup$
    – joka
    Nov 14, 2020 at 19:41
  • 3
    $\begingroup$ @joka I use it myself quite regularly. Here, for example. $\endgroup$
    – Sjoerd Smit
    Nov 14, 2020 at 23:15

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