Lisp has built-in syntax for example in the form of special operators. LET is an example. LET provides bindings for variables: LET a list of

Lisp has built-in syntax for example in the form of special operators. LET is an example. LET provides bindings for variables: LET a list of bindings a sequence of declarations a sequence of expressions (LET ((a 1) (b 2) c) (declare (integer a)) (declare (type (integer 0 100) b) (setq c (+ a b)) (expt c 2)) The EBNF syntax for LET is: let ({var | (var [init-form])}*) declaration* form* DECLARATION and FORM have more syntax. If Lisp sees a LET form which does not use above syntax, then it is a syntax error. A compiler or interpreter will tell you that. The compiler will detect that at compile time. The following forms are all errors: (let a 10 (+ a 10)) (let (a 10) (+ a 10)) ; 10 is not an identifier (LET (((A) 10)) (+ a 10)) ; (a) is not an identifier (let ((a 10)) (+ a 10) (declare (integer a))) ; declaration at wrong place (let ((a = 10)) (a + 10)) ; Lisp has no infix operators...