Re: Making Lua lexically scoped (was: Re: Proper tail recursion)

[ramsdell@... (John D. Ramsdell)]

"Peter Prade" <prade@phenomic.net> writes:

> Jay Carlson comments on John Ramsdell:
> >> By the way, the more I think about the suspected Python method for
> >> making that language lexically scoped, the more I like it.  That is, I
> >> like the idea that a language is lexically scoped, but as sacrifice to
> >> allow efficient implementations, variables become immutable whenever
> >> they are referenced by a closure.
> >This gives me the creeps.  To understand whether something is writable or
> >not you can't just look at its declaration; you have to inspect all of the
> >code inside its defining block.
> 
> I wholeheartedly agree, the current solution at least clearly marks those
> upvalues as something special and readonly.

I believe programs written in a good scripting language should be
easily read by people only casually familiar with the language.  With
the exception of upvalues, I think Lua excels in this respect as it
adopts Pascal-like syntax for control structures whose meaning is just
what one would expect.  Programs that employ upvalues are unlikely to
be understood by casual users.  One needs a manual to understand when
they get their value.  Most people intuitively understand lexical
scoping.  Making variables immutable when they are referenced in
closures puts a burden on the authors of a Lua program, but not on
readers of the program.  I think Lua should be designed to meet the
needs of readers foremost.

John