Re: Elisp lexical-let

[Ken Raeburn <raeburn@raeburn.org>]

On Jul 22, 2009, at 05:11, Daniel Kraft wrote:
> It seemed really hard to me to find at least *basic* information  
> about how the lexbind things works; I did build now an emacs with  
> lexbind from trunk, but so far as I see this is not meant to  
> implement "lexical-let" as the cl package does, but rather allows  
> switching all bindings from dynamic to lexical within one source file.

Oh... I may have seriously misunderstood; sorry about that.  That's  
what comes from not having bothered to look. :-)

In that case, the cl package is probably the thing to look at for now;  
it is used by a bunch of other things in Emacs.  But I do expect  
lexbind is going to get merged in eventually, so keeping that in mind  
for the future would be wise too.

> And checks with the cl package's implementation of lexical-let give  
> the result, that an inner let does the same as if it was another  
> lexical-let; that is, does not revert to dynamic binding but rather  
> sets only the lexical value.
>
> So, what are the opinions regarding lexical-let as an extension  
> construct?  Regarding the behaviour, to me the one described above  
> seems to be a consequence of the implementing with unwind-protect  
> and not necessarily expected -- thus I suggest to implement the  
> version I had in mind, namely that an inner let or argument binding  
> inside a lambda reverts to dynamic binding for that inner scope.   
> This seems more consistent and reasonable to me.

I think you could make an argument for doing it either way.  The  
interesting question would be whether anyone is depending on the  
behavior from the cl package.

Ken