The parser for s-expressions is READ. S-Expressions are just a data syntax and know nothing about the Lisp programming language syntax. Lisp syntax is defined o

The parser for s-expressions is READ. S-Expressions are just a data syntax and know nothing about the Lisp programming language syntax. Lisp syntax is defined on top of s-expressions. The Lisp evaluator sees no parentheses and no text, It would not care if the input text contains )postfix 1 2+( . The reader can actually be programmed to accept that as input. The actual Lisp forms need to be syntax checked then by a compiler or interpreter. There are lots of language with code generators. Lisp does this as core part of the language and can do it at runtime as part of the evaluation machinery.