"Everything as an expression" is concept that exists entirely separate from LISP as a programming language. Eg, in the untyped lambda calculus everything is ind

"Everything as an expression" is concept that exists entirely separate from LISP as a programming language. Eg, in the untyped lambda calculus everything is indeed an expression and it obviously predates LISP. The thing that makes LISPs interesting is that both data and code have the same representation. Manipulating code and data looks the same and that leads to all sorts of interesting meta-programming constructs Also I'm not sure what you mean by "under the hood", but Ruby's internal representation is an abstract syntax tree (as with most languages). That AST bears a resemblance to LISP because LISP is both the language and AST rolled into one, but I would never confuse Ruby for LISP because it has an AST representation.