Typed Structures
Picturing Programs Code
Code in this section requires the installation of an extra package
picturing-programs-typed
, then
(require typed/picturing-programs)
You should also have access to a typed version of the posn-util
.
Defining new structures
A new structure need type information just like a function. There are also some incantations you will want to use.
#:transparent
- Always include this.#:type-name
- Usually include, should be name of struct with a capital letter at the start.
Example:
(define-struct ship ([ name : String ]
[ pos : (Listof Posn) ])
#:transparent
#:type-name Ship)
Functions using structures
A function bn
that takes in a ship and produces an image of a box around
the name would be written like this:
(define (bn [s : Ship]) : Image
(frame (text (ship-name s) 24 "black")))
Copying Structures
Racket has a method called struct-copy for copying a structure and changing some of the entries.
(struct-copy STRUCT-NAME VARIABLE [field NEW-VALUE])
Example:
(define a-ship1 (make-ship "Dingy" (list (make-posn 5 2))))
(define a-ship2 (struct-copy ship a-ship1 [name "Sailboat"]))
Colors
It can be tricky to write the limit function that restricts a number to the range 0 to 255 for use in a color.
(define (limit [n : Integer])
: Byte
(min 255 (max 0 n)))
If you need to handle real number inputs, add in (round (inexact->exact n))
.
Trivia: the order of the inputs matters, check the type signature of
max
.