Lexical environment for functions?

Lexical environment for functions?

[David Kastrup]

I read

    eval is a built-in function in `eval.c'.

    (eval FORM &optional LEXICAL)

    Evaluate FORM and return its value.
    If LEXICAL is t, evaluate using lexical scoping.
    LEXICAL can also be an actual lexical environment, in the form of an
    alist mapping symbols to their value.

    [back]

Does that mean that lexical environments exist only for value cells?  No
function cells?  Because it would seem convenient, if one has some
Lisp-like presentation of a parse tree like XML, to just eval it with a
number of function bindings in place.

Does one need to create an obarray for each kind of interpretation and
reread the input with the changed obarray in place?

-- 
David Kastrup

Re: Lexical environment for functions?

[Stefan Monnier]

> Does that mean that lexical environments exist only for value cells?

Yes, at least for the "native" lexical binding.

> Because it would seem convenient, if one has some
> Lisp-like presentation of a parse tree like XML, to just eval it with a
> number of function bindings in place.

Just like you could simulate the new (eval E ENV) form via
(eval `(lexical-let ,ENV ,E)), you can do the above with
(eval `(cl-flet FENV E)).


        Stefan

Re: Lexical environment for functions?

[David Kastrup]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Does that mean that lexical environments exist only for value cells?
>
> Yes, at least for the "native" lexical binding.
>
>> Because it would seem convenient, if one has some
>> Lisp-like presentation of a parse tree like XML, to just eval it with a
>> number of function bindings in place.
>
> Just like you could simulate the new (eval E ENV) form via
> (eval `(lexical-let ,ENV ,E)), you can do the above with
> (eval `(cl-flet FENV E)).

cl-flet is optimized for compilation rather that interpretation.  So
this is not likely to make eval a good idea for fast interpretation of
parsed expressions.

-- 
David Kastrup