Re: History of lexical scope in Lisp

On 2024-03-15, Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

On Fri, 15 Mar 2024 16:05:37 -0600, Jeff Barnett wrote:
>

Once you have had the programming convenience of using dynamic scope,
you would miss it terribly in a lexical-only language, or worse, in
something like the old FORTRAN assembler-level scope. Another argument
that I have not seen debated but may be significant is that the CL Error
System -- the programming primitives and error class structures don't
make a lot of sense in lexical only. The error mechanisms like catch
have meanings that include phrases such as "while executing this. I'm
available to handle that".

>
Lexical binding has always been understood to apply to references to
definitions of identifiers. Exception handlers are dynamically-installed
(lexical-based exception handling doesn’t make any sense), nevertheless
the names of the defined exceptions being handled are still lexically-
bound.
>
This is how it works in every rationally-designed language.

Names of exceptions (conditions) are not lexically bound in Common Lisp.

They are pervasive, similarly to class names.

Lexically scoped exception handling does make sense, during those
sections of the handling when a lexical scope isn't being abandoned.

If the termination point of an exception is in lexical scope of the
origin, then the case can be made for handling the entire episode
lexically, including the unwinding.

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