DrRacket
This document describes how to setup and use the DrRacket environment for programming in the Racket language in CS 251. Full DrRacket documentation is available on the Racket language website.
Contents
Installation and Startup
CS Linux machines have DrRacket installed. To run it, execute the command drracket
in a terminal.
DrRacket is available for several platforms at https://download.racket-lang.org/ if you want to install it on your own computer.
Interface
The DrRacket window is split into Definitions on the top and Interactions on the bottom.
Create and save files (with a .rkt
extension) in the Definitions
editor. Experiment in the Interactions REPL (read-eval-print loop)
– text typed here is not saved (by default).
File structure
Follow these guidelines when creating new Racket files.
Choose a language (Racket)
Start each Racket file with the line:
#lang racket
to indicate that you are using the Racket language.
If you want to experiment in the Interactions REPL without saving a
file, the Interactions REPL still requires you to choose a language.
If the Interactions REPL has no language selection (it will print an
error about this), add #lang racket
in the Definitions window and
click Run.
Provide definitions
For Racket files you submit (e.g., assignment.rkt
), the second non-comment line must be:
(provide (all-defined-out))
In the Lisp and Scheme languages (Racket’s grandparent and parent),
all top-level definitions are globally visible. Racket adds a module
system. By default, Racket definitions are only visible (in scope)
within a file (module). (We will discuss modules later in the course
with a different language.) provide
makes these definitions
globally visible for our testing system.
Separate testing files
To write tests in a separate file test.rkt
from function definitions
(say, assignment.rkt
), load the definitions from assignment.rkt
in
test.rkt
:
(require "assignment.rkt")
Both files need to start with #lang racket
. Unlike
assignment.rkt
, test.rkt
does not need to provide
anything.
Using DrRacket
For the most part DrRacket is an easy-to-use system with lots of documentation. Here are a few specific notes related to how we will use it:
- Click
Run
to have the Interactions REPL (read-evaluate-print loop) process the current Definitions. - Clicking
Run
loads the Definitions in a fresh Interactions REPL. Any bindings you made in the Interactions REPL will be lost. - The Interactions REPL has history: use Control-↑ (that’s
the up arrow key) to summon previously entered lines. This history
remains available across
Run
(and even across opening and closing DrRacket) even though it does not remain in the environment across these events. - When using a separate testing file as described in the previous
section, click
Run
in the window that shows the testing file. - If you cause infinite recursion (i.e., an expression is taking
long enough to evaluate that you suspect it will run forever), click
Stop
. - The
Tab
key (re-)indents a line properly. You can select multiple lines and hitTab
to indent all selected lines properly. - If you type
)
, DrRacket will replace it with]
if doing so will match a[
. - Typing
Alt-\
on Linux orCommand-\
on a Mac inserts a λ character iflambda
is too much for you. - DrRacket supports many Emacs keybindings. We will use Emacs later in the course, so learning them now is a great idea.
Acknowledgements
This document is adapted from a similar document by Dan Grossman at the University of Washington.