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If I get the function definition with

(setq wrapped-copy (symbol-function 'fn))

how can I make a copy such that I can redefine the same function with a wrapped version? like

(fset 'fn #'(lambda () (wrapped-copy)))

I tried with copy-seq but I think it copies by reference, so the anon function looses the function definition in the wrapped copy

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  • emacs.stackexchange.com/tags/elisp/info
    – Drew
    Commented Feb 1, 2021 at 20:45
  • Unclear what you mean by "redefine" and "wrapped version". fset lets you define an alias, like defalias does. And you're using a variable whose value is a function in function position. Elisp is a Lisp 2, not a Lisp 1, so you would need (lambda () (funcall wrapped-copy)). But as I say, to me it's not clear what you're asking.
    – Drew
    Commented Feb 1, 2021 at 20:48

1 Answer 1

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3

Use funcall or apply:

(setq wrapped-copy (symbol-function 'emacs-version))
(fset 'fn (lambda () (funcall wrapped-copy)))

(fn)
"GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.32, cairo version 1.16.0)
 of 2020-06-15"

Although, in general, I would use an advice for wrapping a function.

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