Re: flet vs cl-flet vs compilation-start

[Michael Heerdegen <michael_heerdegen@web.de>]

Stephen Leake <stephen_leake@stephe-leake.org> writes:

> I'm using compilation-mode to show results from running an external
> program; it produces output that looks like compilation errors (it's
> actually cross-reference info).
>
> Some users would like to preserve output from several calls to the
> external program.
>
> compilation-start does not provide an option for this; it calls
> (erase-buffer) unconditionally.
>
> So someone suggested this hack:
>
> (require 'cl)
> (flet ((erase-buffer nil (goto-char (point-max))))
>     (compilation-start ... ))
>
> That works, but produces byte-compiler warnings about cl and flet.
>
> So I tried:
>
> (require 'cl-lib)
> (cl-flet ((erase-buffer nil (goto-char (point-max))))
>     (compilation-start ... ))
>
> This does _not_ work. Apparently in the "flet" case, the local
> definition of 'erase-buffer' overrides the global one, but in the
> 'cl-flet' case it does not.

The cause is that the function bindings created by cl-flet and cl-labels
have lexical scope.  And that is documented.

As already has been mentioned, as a last resort, use cl-letf in such
cases.


Michael.