Shadowing variables in autoVar/autoLet

[edemaine]

I recently bumped into CoffeeScript Madness which reminded me of the counterintuitive behavior in CoffeeScript (and autoVar/autoLet that mimic it) that assigning a variable in an outer scope can modify the behavior of functions defined (deep) within that scope. There are also counterarguments. In practice I've found it a convenient but very dangerous feature.

Scoping was changed in other languages like CokeScript and LiveScript, which both use := to mean "assign this variable from an outer scope" (just CoffeeScript's =), and otherwise make new vars in each function scope (unlike CoffeeScript). Obviously we can't use := in Civet though.

I've long been thinking of adding a flag like "civet autoVar shadow" that automatically makes a var at each function scope, but allows some way to escape and access variables at a higher scope. What came to my mind was Python's nonlocal keyword, or maybe another name like outer, as in:

"civet autoVar shadow"
x = 5
function increment()
  outer x
  x++
function myOwnX()
  x = 10
↓↓↓
var x
x = 5
function increment()
  return x++
function myOwnX()
  var x
  return x = 10

I'm not sure what's best, though, so I thought I'd open it up to discussion here.