Lisp is one of the most significant early AI programming langauges, known for its heavy use of brackets. Lisp stands for "List processing" and the language is heavily influenced by the lambda calculus. Lisp has several dialects including Scheme. Lisp is an early functional programming lanugage although not a pure functional language as it has updatabale variables and state.
Links:
tutorialspoint.com: Online Lisp Compiler