Introduction to Artificial Intelligence Lisp Ruth Bergman Fall

Introduction to Artificial Intelligence Lisp Ruth Bergman Fall 2002

LISP • LISP (List Programming) – invented by John Mc. Carthy, Stanford, 1958 – interpreted and compiled language – many firsts (interpreter, garbage collection, debugger. . ) • Basic structure of LISP is the list – atoms • quoted representation – – – cons nil car cdr null print representation

LISP Functions • Lisp expressions – quoted symbol – variable – functions • The easiest way to understand how Lisp operates is to understand the interpreter: – (loop (print (eval (read))) • read an expression (atom, quoted symbol, or list) • evaluate that expression • print the result

LISP Functions • Lisp expressions – quoted symbol – variable – functions • Functions are prefix notation – cons, cdr, cdddr. . . – arithmetic – list manipulations (append, list, cons) • (append ‘(a b) ‘(c d)) • (list ‘(a b) ‘(c d)) • (cons ‘(a b) ‘(c d)) – other lists (subst, last, length)

LISP Variables • Variables can be declared, or created dynamically – (set ‘a ‘b) – (setq a ‘b) – (setf a ‘b) • We can even force evaluation – (setf a ‘b b ‘c) – (eval a)

More Functions/Predicate • (defun fact (n) (if (= n 1) 1 (* n (fact (1 - n))))) – values passed by value (copies) – variables are bound or free – variables are lexically scoped (dynamic is possible) • • • numberp atom listp evenp, oddp and/or/not

Functions are Data • Notice that a function is just a list; we can manipulate it like data – (setq fun ‘fact) – (funcall fun 3) 6 – (apply #’fact ‘(3)) • We can define “anonymous” procedures – (funcall ‘(lambda (x) (list x)) 3) (3) – (funcall (list ‘lambda ‘(x) ‘(list x)) 3) • We can also define local variables – (defun foo (x) (let ((a 1) (b 3)) (setq b (* x b)) (list a b x))) • There are lots of other “functions” – map – reduce

Some exercises • Define – – – reverse flatten member union intersection difference