DAY 3 OF
BOOTSTRAP
STRINGS AND IMAGES
S I T I N YO U R PA I R S . G R A B YO U R C H R O M E B O O K S
A N D L O G I N TO W E S C H E M E . O R G
STRINGS AND IMAGES
One of these things is not like the other…
• 12
-53
“hello”
4.9
A string is anything between quotation marks.
What happens if you put quotes around multiple words?
Around numbers?
Try entering different strings into the Interactions window.
2
How would you convert this to code?
star
(star 5050 “solid”
“red”)
“solid” “red”
A new function called star.
(star has been defined previously in the computer program)
The addition function + takes in two Numbers
and produces a Number
The function called star takes in a number and two strings
and produces a new type of data, called an Image.
(star 50 “solid” “red”)
Try this in your interactions window.
What is the datatype of each of the values listed below
Number String or Image?
Domain of a function is its input or the data the function
expects.
Examples:
• The function + has a domain of two numbers
• The function – has a domain of two numbers
• The function star has a domain of a number and two strings
We need to keep track of the required inputs for each function
By keeping a list of all the functions in a language, and
their Domains, programmers can easily look up how
each function is used.
It’s also important to keep track of what each function
produces.
• For example, a program wouldn’t use star if they were trying to produce a
Number, because star only produces Images.
The Range of a function is the data that the function
produces.
CONTRACTS
A contract has three parts:
– The Name
• Example: Star
– Domain
• Example: A number and Two Strings
– Range
• Example: Image
The Contract is: ; star: Number String String  Image
Write the contract for star in the back
page of workbook
Here is the contract for a new function rectangle
; rectangle: Number Number String String  Image
•
•
•
•
What is the Name of this function?
How many things are the Domain of this function?
What is the type of each thing in the Domain?
What is the Range of this function?
Write the contract for rectangle in your contracts page
MORE IMAGE FUNCTIONS
; circle :
Number String String
 Image
; ellipse:
Number Number String String  Image
; triangle:
Number String String
 Image
; rectangle: Number Number String String  Image
; text:
String Number String
 Image
; rotate :
; scale:
Number Image
Number Image
…and dozens more!
 Image
 Image
12
(3+4)=7
What would the contract be of this expression?
; + : NUMBER NUMBER  NUMBER
Write the contract for +, -, *, / on your contracts page?
CONTRACT OR CODE?
; triangle : Number String String  Image
(triangle 100 “outline” “blue”)
; square : Number String String  Image
(square (+ 200 5) “solid” “red”)
Figure out the domain and range
of the following:
rhombus
right-triangle
radial-star
star-polygon
Write the contract for each in your contracts page.
IMAGES CAN BE INPUTS
You can use the function: flip-horizontal to flip your image from left to right
CONTRACT
CODE
; flip-horizontal : Image  Image
(flip-horizontal (right-triangle 50 20 “outline” “red))
Convert the racket code to a contract
and add to your contract page
(flip-vertical (triangle 50 “outline” “orange”))
(scale 2 (text “resize” 10 “purple”))
(rotate 45 (text “spin” 30 “green”))
Experiment with the code in the interactions window