LISP Functions and Control Structures, Slides of Programming Languages

Download LISP Functions and Control Structures and more Slides Programming Languages in PDF only on Docsity! Functions > (reverse L) ; reverses a list (C B A) > (length L) ; returns the length of list L 3 List has elements (A B C) Docsity.com Predicates • A special function which returns NIL if the predicate is false, T or anything other than NIL, otherwise • We can use the following operators to build the predicates – =, >, <, >=, <= for numeric values – eq or equal for others – atom: test if x is an atom – listp: test if x is a list – Also number, symbolp, null Docsity.com > (setf operation ‘area L 100 W 50) > 50 > (cond ((eq operation ‘perimeter) (* 2 (+ L W))) (eq operation ‘area) (* L W)) (t ‘i-do-not-understand-this) ) ) > 5000 Docsity.com • A list can be viewed as a set whose members are the top elements of the list > (member 'b L) (B C) > (member ‘b (cons 'b L)) (B A B C) > (member x L) NIL ; if no, returns NIL > (union L1 L2) ; returns the union of the two lists > (intersection L1 L2) ; returns the intersection of the two lists > (set-difference L1 L2) ; returns the difference of the two lists Set Operations Test if symbol b is a member (a top element) of L; if yes, returns the sublist of L starting at the first occurrence of symbol b List L has elements (A B C) Docsity.com Defining LISP functions (defun func-name (arg-1 ... Arg-n) func-body) Example: > (defun y-plus (x) (+ x y)) ;definition of y-plus > (setq y 2) > (y-plus 23) 25 • Local and global variables: local variables are defined in function body • Function returns the value of last expression in its body Docsity.com