Elisp flet construct

[Daniel Kraft]

Hi all,

in the %nil thread a suggestion was brought up to support the `flet' 
construct (and `flet*' as well, if we choose to do so at all, I favour) 
in Guile's upcoming elisp implementation that behaves just like a let 
for function-slot bindings, enabling dynamic scoping for them.

It is no "official" elisp construct, but according to what I heard 
there, can be useful at some times (I guess the use is mainly to locally 
alter bindings of standard functions for some code executed without a 
risk of permanently messing things up).  So I don't know how you regard 
addition of "extensions"...?

From an implementation point of view, I see both an argument against 
and in favour of this extension:

* As implemented at the moment, it would be fairly easy to add 
flet/flet* to the compiler.

* If we do not implement flet, we can implement the function-slots 
without indirection via fluids but rather use the Guile symbol bindings 
directly.  This is for sure a simplification especially performance 
wise, but I can't say how much it really affects.  Most bindings in use 
are, I guess, variables, so we save the fluid-references only in a 
fraction of cases.

Any comments welcome, so we can decide upon this.

Thanks,
Daniel

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