The creator of Ruby admitted that implicit local was "the single biggest design flaw in Ruby." http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/42266

The creator of Ruby admitted that implicit local was "the single biggest design flaw in Ruby." http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/42266 http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/... I think what most people really want is to avoid implicit scoping altogether. But then you need a special keyword to access global environment symbols. That's a little awkward in Lua because the "require" function used to import libraries is just a regular function in the global environment table (which is otherwise just a plain table), and so `local string = require"string"` works because undeclared symbols become an index into the global environment table. And libraries like "string", "math", etc are also usually prepopulated. A lot of people do `require"strict"` (or if you want to be pedantic, `local _ENV = require"strict"`) early in a Lua source file, which modifies the global environment to throw a runtime error instead of returning `nil` for undefined symbol lookups. (There are various versions of the strict library floating around; it doesn't come with stock Lua.) If would be better if this was a static check in the language itself. That, too, isn't a difficult addition (it could even be added to a strict library, or you could overload require), but defaults matter when it comes to nitpicking languages, I guess. Maybe in Lua 5.5 or 6.0 this change will be made. Though, statically-checked scoping isn't as as straight-forward as you'd think given Lua's common use as a fast-and-loose sandbox for running user code, ad hoc business logic modules, etc, where a lot of preamble boilerplate can seem overly complex. But the upside to Lua having a loose commitment to backward compatibility is that it's much easier to experiment with these sorts of changes and keep iterating until they nail down a solid construct. For example, compare setfenv/getfenv in Lua 5.1 with the lexical _ENV construct in Lua 5.2.