You might want to reread the Wikipedia article and tone down a bit: Check out the abstract syntax tree on the right: https://en.wikipedia.org/wiki/Abstract_

You might want to reread the Wikipedia article and tone down a bit: Check out the abstract syntax tree on the right: https://en.wikipedia.org/wiki/Abstract_syntax_tree It has a node which is a BRANCH and which has three relations CONDITION, IF-BODY, ELSE-BODY. In an s-expression this is just (if (> a b) (setq a (- a b)) (setq b (- b a)) Thus there is no representation that IF is a branching expression, there is no representation that A and B are variables. There is no representation that > is a compare op. And so on. The s-expressions are just nested lists of tokens without any idea what the tokens refers to or what language construct it stands for. All we know is what the tokens are and a hierarchy. A is a symbol, but what kind we don't know: it could be a data object, a variable name, a function name, a goto tag, a name of a class, a name of a type, ...). In the abstract syntax tree the > is identified as a compare op, IF is identified as a branch, A is identified as a variable identifier, ... The Lisp reader also does not create that information. It just creates a data structure, which could be anything, any kind of data.