On Tue Oct 4 2016 Stefan Monnier wrote:
> There are two ways to do that with lexical-binding:
> - use (eval <form> `((<var1> . ,<val1>) (<var2> . ,<val2>) ...)
>   which will not give the exact same behavior but works well in many
>   cases (i.e. depends on the code put in diary-date-forms).
> - use
>     (defvar <var1>) (defvar <var2>) ...
>     (let ((<var1> <val1>)
>           (<var2> <val2>)
>           ...)
>       (eval <form> t))
>   which will preserve backward compatibility.

Thank you, I did not know that! - It appears to me that the first
approach is the cleaner way to go.  So I've tested it with
bbdb-anniv.el, and it seems to do exactly the right thing.  Under
what circumstances could there be a problem?  (The forms in
diary-date-forms are lists containing symbols and strings.  Then
`eval' is applied to the list elements in order to replace the
symbols by their let-bound values.  So there is nothing fancy
happening here.  Possibly there is yet a completely different
strategy for this problem?  I just copied the relevant code from
diary-list-entries-2, assuming that this should be the most reliable
strategy for bbdb-anniv even if I do not know too much about

Actually, I am a bit confused about the second approach you
suggested.  I believe I understand its logic, though I find it odd
to use defvar in such a context.  Interestingly, the elisp manual
says about `defvar':

     If SYMBOL is already lexically bound (e.g., if the ‘defvar’ form
     occurs in a ‘let’ form with lexical binding enabled), then ‘defvar’
     sets the dynamic value.  The lexical binding remains in effect
     until its binding construct exits.  *Note Variable Scoping::.

This suggests to me that in your second approach the defvar's could
also go inside the let, which appears rather odd to me.  Or am I
misinterpreting this paragraph?  What would be an example for this
usage of defvar in a let form?

Thanks again,


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