Racket CSC270 Pepper major portions credited to http://learnxinyminutes.com/docs/racket/

Screen Functions Read in a variable from the screen (read var) example : (read n) write a variable to the screen: just put the variable name final result of all functions write to the screen literal alone will write to the screen Example: "What is your name?" (define n (read )) n (string-append "hello " (symbol->string n))

String Functions Put 2 strings together: (string-append "cat" "dog") Returns "catdog" Pick out one character knowing the index (string-ref "cat" 1) Returns "a" Put a string together in printf fashion: (format " ~a are number ~a " "cats" 1) (printf " ~a are number ~a " "cats" 1) Both return "cats are number 1"

Construct a pair (small list) Make a pair (cons 3 4 ) Pull out the first element of a pair (car (cons 3 4)) Pull out the second element of a pair (cdr (cons 3 4)) Make one side of pair empty (cons null null ) Make an empty pair '() or null

Lists Define a list: linked lists of pairs with one side being the list item and the other being the rest of the list, that ends in null or () (cons 1 (cons 2 (cons 3 null))) (list 1 2 3) quote for the literal value '(1 2 3) (build-list 10 values) to get 0 to 10

Add items to a list add items to a list (cons 4 '(1 2 3 )) (append '(1 2) '(3 4))

List Functions Do the same thing to every item in the list (map add1 '(1 2 3)) gives '(2 3 4) Apply one list to another list of the same number of items (map + '(1 2 3) '(10 20 30)) extract only even (filter even? '(1 2 3 4)) gives '(2 4) count only even (count even? '(1 2 3 4)) gives 2 take the first n items (take '(1 2 3 4 ) 2) gives '(1 2 ) drop the first n items (drop '(1 2 3 4 ) 2) gives '(3 4) is it a member? (member 'dog '(cat dog rat)) gives #t first member value (first '(3 4 5)) gives 3 get number of elements (length '(3 4 5)) gives 3

Define Functions using Lists (define (addlist mylist2) (cond [ (eq? mylist2 null) 0] [ else ( + (first mylist2 ) (addlist (drop mylist2 1)))])) (define list1 (list 8 2 5)) (addlist list1) (addlist (cons 1 (cons 2 (cons 3 null))) )

Mapping Map – run the function for each item in the list (map sqrt '(4 16 25)) Apply one list to another list of the same number of items with a function taking in 2 parameters (map + '(1 2 3) '(10 20 30)) Use your own functions: (define (add3 x) (+ x 3)) (map add3 '(1 2 3))

Important Concepts Create lists Map against lists Recurse through lists until empty