Top half is definitions area and bottom half is interactions area
Instructions to compute are entered in the definitions area while outputs of computation are displayed in the interactions area
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Writing programs in Dr Racket:
Programs consists of expressions. In the context expressions begin with a ( and end with )<\li>
Each set of parenthesis consists of an operator followed by one or more operands.
Operators may be numbers, text, boolean values, images or other expressions.
Operators with numerical operands (or expressions that return numbers) include:
+, -, /, *
number->string
>, <, =
Operators with string (text) operands (or expressions that return strings) include:
string-append, string-length, string->number
Operators with boolean (#true, #false) operands (or expressions that return booleans) include:
and, or, not
Operators with image operands (or expressions that return images) include:
image-height, image-width
Images:
Expressions can be used to generate images, e.g. (circle 10 "solid" "red") will create an solid red circle with a diameter of 10, (rectangle 10 15 "outline" "blue") will create an empty rectangle with a blue outline and a width of 10 and a height of 15
Images can be composed using the operation overlay e.g. (overlay x y) will overlay the image x on the image y
A grid can be constructed using the operation empty-scene e.g. (empty-scene x y) will produce a grid with an width of x and a height of y. The origin will sit at the top left hand corner of the grid