The Scope class regulates lexical scoping within CoffeeScript. As you
generate code, you create a tree of scopes in the same shape as the nested
function bodies. Each scope knows about the variables declared within it,
and has a reference to its parent enclosing scope. In this way, we know which
variables are new and need to be declared with var, and which are shared
with the outside.
Import the helpers we plan to use.
{extend, last} = require './helpers'