The principal data structure of Lisp is a list which is written like this: (a b c d). Like the article mentions, when you see Lisp code you're in fact reading the same list syntax, only that, when the list itself is not quoted, the "a" is evaluated as a function, which is why (+ 1 2) behaves the way it does. If you quote the list by saying "'(a b c d)" then it is a list of symbols, so "'(+ 1 2)" does nothing.
Hence, Lisp code is made of nested lists. When you think further about it, it means that Lisp metaprogramming facilities may do things just with plain list manipulation functions! So it's not about metaprogramming itself, it's that it's incredibly easy. This is what people refer as "code as data" and "homoiconicity" and so on.
Hence, Lisp code is made of nested lists. When you think further about it, it means that Lisp metaprogramming facilities may do things just with plain list manipulation functions! So it's not about metaprogramming itself, it's that it's incredibly easy. This is what people refer as "code as data" and "homoiconicity" and so on.