Lisp is already made of trees. A Lisp program is a pre-order traversal of the abstract syntax tree of a yacc'ed program in another programming language. This

Lisp is already made of trees. A Lisp program is a pre-order traversal of the abstract syntax tree of a yacc'ed program in another programming language. This fact is WHY Lisp is powerful. By eliminating yaccing you can create new syntax on the fly without having to recompile your compiler.