1. Racket
CSC270 Pepper
major portions credited to

2. 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))

3. 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"

4. 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

5. 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

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

7. 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) '( ))
extract only even (filter even? '( )) gives '(2 4)
count only even (count even? '( )) gives 2
take the first n items (take '( ) 2) gives '(1 2 )
drop the first n items (drop '( ) 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

8. 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))) )

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

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