local-by-default revisited

[Reuben Thomas <rrt@...>]

What follows is another "local by default" proposal. IMO it's simpler,
less obtrusive and yet gives better results than other proposals. It's
intended for Lua 4.1.

The changes are:

1. Add a new keyword "outer" which works like "local", except that it
   declares the given name to refer to the innermost variable of the
   same name in an enclosing function or, if there is none, to a
   global of the same name (even if none currently exists).

2. The first assignment to a variable in a function implicitly acts as
   a "local" declaration unless it has already been declared in that
   function, explicitly or implicitly. Assignment outside a function
   works as at present, as does assignment to table elements.

Note:

a. The ability to do configuration file style global assignment is
   retained, at the cost of making assignment inside functions work
   differently from outside. In practice this shouldn't be a problem,
   as few Lua scripts contain complex code at the top level. If you
   need local variables in top-level code, you must simply declare
   them as at present.

b. The only change to the syntax is the addition of "outer".

c. The only semantic change is to the meaning of assignment within
   functions.

d. Assignments only make the variable local where they occur, rather
   than for the whole function. This agrees with the principle of
   least surprise: you don't have to read an entire function to find
   out whether a given variable is local (and nor does the compiler,
   so the implementation is simple).

[I've put this on the Wiki too as LocalByDefault under
FeaetureProposals.]

-- 
http://sc3d.org/rrt/ | competent, a.  underpromoted