[kazinator]

Or rather, one needs to learn which constructs destructively manipulate a global environment, and which perform lexical binding.

In Python, an inner def will lexically bind a function, creating a closure. Python is not less dynamic than Ruby.

In Common Lisp, a defun inside a defun will behave similarly to Ruby; but if you want lexically scoped local functions, you use a different operator, namely flet or labels.

Scheme has a define which is lexical: it brings a lexical identifier into the scope for forms which follow.

Lexically scoped items, even in a dynamic language, in fact can be "cast in stone when you press the compile button"; they are cast in that stone which is the entire compiled environment of the surrounding function.