My name: Doug Salvati
I used the draw library in order to learn how to export to PDF file, which is a feature that will be useful for showing the results of our final project. In this example, I create a closure representing a book, with methods that allow the user to write paragraphs into the book. The result is a PDF file posted in the current working directory.
An interaction looks like this:
(define myBook (make-book "exploration2.pdf"))
((myBook 'open))
((myBook 'write) mypara)
((myBook 'write) mypara2)
((myBook 'write) mypara3)
((myBook 'turn-page))
((myBook 'write) mypara3)
((myBook 'write) mypara3)
((myBook 'write) mypara3)
((myBook 'close))
Here is a look at the first page of the resulting output before the 'turn-page command:
To open the book, close the book, and turn the page, special calls are made to draw procedures that manage the PDF.
Write, on the other hand, is a procedure I made to write a paragraph (an object created using make-paragraph) to the book:
(define (write-paragraph para)
(if (null? para)
(newpara)
(begin (send book draw-text (car para) col row)
(call-with-values (lambda () (send book get-text-extent (car para))) update-position)
(write-paragraph (cdr para)))))
It is a tail-recursive procedure which prints the word to the file, increments the position of the cursor based on the length of the word, and then recurses on the rest of the words. At the end, a special update function newpara is called to set up spacing and indentation for the next paragraph the user may write.
All of the position updating is done using variables and procedures I wrote. When I started with exploration2global.rkt, all variables and functions were in the global environment. However, I quickly realized that only a few of the functions: open-book, close-book, turn-page, and write-paragraph, were useful to the user. Furthermore, if you tried to write two books at once, the global variables used by the functions would get all corrupted. So, I re-implemented the assignment in exploration2.rkt using a closure and a dispatch function, similar to the bank accounts in SICP and PS4. This is a better model, and it makes my sample interactive session simpler for the user. This is how the four possible commands are processed:
(lambda (m)
(cond ((eq? m 'open) open-book)
((eq? m 'turn-page) turn-page)
((eq? m 'close) close-book)
((eq? m 'write) write-paragraph)
(else (error "Unknown request")))))
Due to the use of lambda rather than define, this is actually the return value for make-book, meaning a book is actually a procedure! And, it returns procedures that the user wants to use.
Note that paragraphs are made to be list of words, for instance:
(define mypara (make-paragraph "We're" "all" "mad" "here."))
It may seem cumbersome to do this way, but in the end we will be drawing a list of objects which contain musical notes, so this format will be more natural down the road.