PL: Resources

Class Notes

These are the class notes files. In some places they are in pretty raw form, intended mainly for reference, code examples etc. They are not a substitute for taking notes in class, and they certainly cannot compensate for not coming in. Also, they are not guaranteed to cover all of the material that was presented in class. What they do get you is avoiding the hassle of trying to copy this stuff that you see it in class.

Lecture #1
  ? Tuesday, January 12th
Intro to CS4400/CS5400
Intro to Programming Languages
Lecture #2
  ? Tuesday, January 12th
Intro to Racket
Side-note: “Goto Statement Considered Harmful”
Quick Intro to Racket
Lists & Recursion
Lecture #3
  ? Tuesday, January 19th
Some Style
Tail calls
Note on Types
Side-note: Names are important
Lecture #4
  ? Tuesday, January 19th
BNF, Grammars, the AE Language
Simple Parsing
The match Form
Semantics (= Evaluation)
Side-note: Compositionality
Implementing an Evaluator
Lecture #5
  ? Tuesday, January 26th
Implementing The AE Language
Intro to Typed Racket
Lecture #6
  ? Tuesday, January 26th
Bindings & Substitution
WAE: Adding Bindings to AE
Evaluation of with
Lecture #7
  ? Tuesday, February 2nd
Evaluation of with (contd.)
Formal Specs
Lazy vs Eager Evaluation
de Bruijn Indexes
Lecture #8
  ? Tuesday, February 2nd
Functions & Function Values
Implementing First Class Functions
The FLANG Language
Introducing Racket’s lambda
Using Functions as Objects
Lecture #9
  ? Tuesday, February 9th
Using Higher-Order & Anonymous Functions
Side-note: “Point-Free” combinators
Substitution Caches
Implementation of Cache Functionality
Formal Rules for Cached Substitutions
Evaluating with Substitution Caches
Lecture #10
  ? Tuesday, February 9th
Dynamic and Lexical Scopes
Dynamic versus Lexical Scope
Implementing Lexical Scope: Closures and Environments
Fixing an Overlooked Bug
Lexical Scope using Racket Closures
Lecture #11
  ? Tuesday, February 16th
More Closures (on both levels)
Types of Evaluators
Feature Embedding
Recursion, Recursion, Recursion
Recursion without the Magic
The Core of make-recursive
Denotational Explanation of Recursion
The Y Combinator
The main property of Y
Lecture #12
  ? Tuesday, February 16th
Typing the Y Combinator
Lambda Calculus — Schlac
Church Numerals
Lecture #13
  ? Tuesday, February 23rd
More Encodings
Alternative Church Encoding
Recursive Environments
Lecture #14
  ? Tuesday, February 23rd
Recursion: Racket’s letrec
Implementing Recursion using letrec
Implementing rec Using Cyclic Structures
Boxes and Mutation
Types for Boxes
Boxof’s Lack of Subtyping
Lecture #15
  ? Tuesday, March 1st
Implementing a Circular Environment
Variable Mutation
State and Environments
Implementing Objects with State
Lecture #16
  ? Tuesday, March 1st
The Toy Language
Compilation and Partial Evaluation
Lecture #17
  ? Tuesday, March 15th
Lazy Evaluation: Using a Lazy Racket
Lazy Evaluation: Some Issues
Lazy Evaluation: Shell Examples
Lecture #18
  ? Tuesday, March 15th
Lazy Evaluation: Programming Examples
Side Note: Similarity to Generators and Channels
Call by Need vs Call by Name
Example of Feature Embedding
Implementing Laziness (in plain Racket)
Lecture #19
  ? Tuesday, March 22nd
Sloth: A Lazy Evaluator
Getting more from Sloth
Implementing Call by Need
Lecture #20
  ? Tuesday, March 22nd
Side Effects in a Lazy Language
Designing Domain Specific Languages (DSLs)
Side-note: WSJ on the proliferation of PLs
Syntax Transformations: Macros
Lecture #21
  ? Tuesday, March 29th
Macro Problems
Complexity of S-expression transformations
Scoping problems
Scheme (and Racket) Macros
Meta Macros
Lazy Constructions in an Eager Language
Recursive Macros
Another example: a simple loop.
Lecture #22
  ? Tuesday, March 29th
Problems of syntax-rules Macros
Racket’s “Low-Level” Macros
Solving the syntax-rules problems
Breaking Hygiene, How Bad is it?
Macros in Racket’s Module System
Defining Languages in Racket
Lecture #23
  ? Tuesday, April 5th
Macro Conclusions
Side-note: macros in mainstream languages
Lecture #24
  ? Tuesday, April 5th
What is a Type?
Our Types — The Picky Language
Typing control
Extending Picky
Implementing Picky
Lecture #25
  ? Tuesday, April 12th
Implementing Picky (contd.)
Typing Recursion
Extending Picky with recursion
Typing Data
Judgments for recursive types
“Runaway” instances
Type soundness
Explicit polymorphism
Polymorphism in the type description language
Type judgments for explicit polymorphism and execution
Explicit polymorphism conclusions
Lecture #26
  ? Tuesday, April 12th
Web Programming
Basic web programming
Continuations: Web Programming
Simulating web reading
More Web Transformations
Transforming a recursive function
Using sum/k
Converting stateful code
Lecture #27
  ? Tuesday, April 19th
Converting higher order functions
Highlevel Overview on Continuations
An Automatic Continuation Converter
Continuations as a Language Feature
Lecture #28
  ? Tuesday, April 19th
Continuations in Racket
Playing with Continuations
The Ambiguous Operator: amb
Delimited Continuations
Continuation Conclusions
Lecture Notes, single file
  ? Tuesday, April 19th
If you find a single file format more convenient.
(Also, as a plain text file.)




We will use the Racket environment extensively. DrRacket, the major component of Racket, will be used to develop code, debug, and submit homework. CCS computers have an updated version installed (available on both Unix and Windows). To use it on your own machine, get it from the Racket website. Binary installers exist for all major operating systems, and the course work will be platform independent.

Racket has a system for distributing software bundles that will be used to get a course-specific plugin. This packages both specific functionality for each homework, and an integrated tool for homework submissions. Once you have Racket installed, download the plugin package, and use the “Setup PLT” application to install it. You can also use “Install .plt File” in the File menu, and enter the URL for the plugin.

Note: The handin server uses a dedicated port for communication. You need to work from a network that does not restrict this port — for example, if you use Northeastern’s ‘NUwave-guest’ network, then you will not be able to connect to the server. ‘NUwave’ (which requires you to authenticate through myNEU) does not have this restriction.

To set-up your account:

Additional software may be used later in the course.

Piazza Group

There is a piazza group for this course at The piazza group is the main medium for discussions, questions, announcements etc. You should use it if you have any questions, so others can benefit from the discussion as well. If you want to ask a question that involves showing your solution code, make sure that you choose the “private” option. Do not to post any homework code on the piazza group without using the “private” option. Direct emails to the course staff should be your last resort. Consult the Email and Piazza Group Policies handout for further details about piazza group posts and emails.

Note that you do not need to request to be subscribed to the mailing list — you will get added after you register with the submission server.

On-line books and other materials

There are lots of Racket and Scheme books on-line, a few good ones are:

You can also find some good on-line courses: In addition, there are lots of additional Scheme-related references at