CS 3540: Using Dr. Racket's sdraw Package

Using Dr. Racket's sdraw Package

Drawing Box-and-Pointer Diagrams in Dr. Racket

In Session 4, we learn to draw box-and-pointer diagrams to help us understand Racket lists, including the how cons and list work.

You may want to practice drawing box-and-pointer diagrams. How can you know if your diagrams are correct?

With the sdraw package, Dr. Racket can help by drawing a box-and-pointer diagram for any Racket list, right in the Interactions pane.

If you would like to use sdraw, read on to learn how to install and use the package.

Installing the sdraw Package

sdraw is a third-party package for Dr. Racket, so we have to install it.

Step 1: Select Install Package... on Dr. Racket's File menu:

a screenshot of selecting the Install Package option on Dr. Racket's File menu — Click on the image to enlarge in a new tab

Step 2: Copy this string:

https://github.com/jackrosenthal/sdraw-racket.git

and paste into the Package Source field of the window that pops up:

a screenshot of entering the location of sdraw's source code into the Package Source field oof the installation window — Click on the image to enlarge in a new tab

Step 3: Press the Install button. It will take a few seconds for Dr. Racket to download and install the source code and documentation for the package.

You are all set.

Using the sdraw Package

To use the sdraw package, we use require to import it into a file or interaction. Then we call the sdraw function to draw a box-and-pointer diagram for a list.

For example, to draw the box-and-pointer diagram for the list '(a (b c) d), we can do the following:

(require sdraw)
(sdraw '(a (b c) d))

a screenshot of requiring the sdraw package in an interaction and calling the sdraw function to draw a box-and-pointer diagram — Click on the image to enlarge in a new tab

Notice that by default, sdraw draws the empty list explicitly as a pointer to (). If that is okay with you, then you are set. If you would like to the diagrams with null pointers, read on.

Customizing sdraw's Output

The sdraw function accepts a number of keyword arguments that customize the way it draws its diagrams.

You may have used keyword arguments in Python to customize the print function, such as to change the end-of-line character (end='') or to write to a file (file=filehandle).

To draw box-and-pointer diagrams the way we do in class, with null pointers in the last cons cell of a list, we need to pass the #:null-style '/ keyword argument to sdraw. For example:

(require sdraw)
(sdraw '(a (b c) d) #:null-style '/)

a screenshot of calling the sdraw function with a #:null-style parameter to draw diagrams with null pointers — Click on the image to enlarge in a new tab

Customizing sdraw's Output Once and For All

If you would like to draw this sort of box-and-pointer diagram without having to call sdraw with the extra parameter every time, download the file draw-boxes.rkt. It creates a new version of the function with null pointers as the default.

Simply place the file in your working folder, and require it into Racket instead of the package:

a screenshot of using the local draw-boxes package to draw diagrams — Click on the image to enlarge in a new tab

And now you really are all set!

More on the sdraw Package

If you would like to learn more about the sdraw package, and especially more ways to custom the diagrams it draws, visit the package's documentation page.