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 10th
Intro to CS4400/CS5400
Intro to Programming Languages
Intro to Racket
Side-note: “Goto Statement Considered Harmful”
Lecture #2
  ? Tuesday, January 10th
Quick Intro to Racket
Lists & Recursion
Some Style
Lecture #3
  ? Tuesday, January 17th
Some Style (contd.)
Tail calls
Note on Types
Side-note: Names are important
BNF, Grammars, the AE Language
Simple Parsing
The match Form
Lecture #4
  ? Tuesday, January 17th
Semantics (= Evaluation)
Side-note: Compositionality
Implementing an Evaluator
Implementing The AE Language
Intro to Typed Racket
Lecture #5
  ? Tuesday, January 24th
Bindings & Substitution
WAE: Adding Bindings to AE
Evaluation of with
Lecture #6
  ? Tuesday, January 24th
Formal Specs
Lazy vs Eager Evaluation
de Bruijn Indexes
Functions & Function Values
Implementing First Class Functions
Lecture #7
  ? Tuesday, January 31st
Implementing First Class Functions (contd.)
The FLANG Language
Lecture #8
  ? Tuesday, January 31st
Introducing Racket’s lambda
Using Functions as Objects
Using Higher-Order & Anonymous Functions
Side-note: “Point-Free” combinators
Substitution Caches
Implementation of Cache Functionality
Formal Rules for Cached Substitutions
Lecture #9
  ? Tuesday, February 7th
Evaluating with Substitution Caches
Dynamic and Lexical Scopes
Dynamic versus Lexical Scope
Lecture #10
  ? Tuesday, February 7th
Implementing Lexical Scope: Closures and Environments
Fixing an Overlooked Bug
Lexical Scope using Racket Closures
More Closures (on both levels)
Lecture #11
  ? Tuesday, February 14th
Types of Evaluators
Feature Embedding
Recursion, Recursion, Recursion
Recursion without the Magic
Lecture #12
  ? Tuesday, February 14th
The Core of make-recursive
Denotational Explanation of Recursion
The Y Combinator
The main property of Y
Typing the Y Combinator
Lambda Calculus — Schlac
Church Numerals
Lecture #13
  ? Tuesday, February 21st
Church Numerals (contd.)
More Encodings
Alternative Church Encoding
Lecture #14
  ? Tuesday, February 21st
Recursive Environments
Recursion: Racket’s letrec
Implementing Recursion using letrec
Implementing rec Using Cyclic Structures
Boxes and Mutation
Types for Boxes
Boxof’s Lack of Subtyping
Implementing a Circular Environment
Lecture #15
  ? Tuesday, February 28th
Variable Mutation
State and Environments
Implementing Objects with State
The Toy Language
Lecture #16
  ? Tuesday, February 28th
Compilation and Partial Evaluation
Lecture #17
  ? Tuesday, March 21st
Compilation and Partial Evaluation (contd.)
Lazy Evaluation: Using a Lazy Racket
Lecture #18
  ? Tuesday, March 21st
Lazy Evaluation: Some Issues
Lazy Evaluation: Shell Examples
Lazy Evaluation: Programming Examples
Side Note: Similarity to Generators and Channels
Call by Need vs Call by Name
Example of Feature Embedding
Lecture #19
  ? Friday, March 24th
Implementing Laziness (in plain Racket)
Sloth: A Lazy Evaluator
Lecture #20
  ? Tuesday, March 28th
Getting more from Sloth
Implementing Call by Need
Side Effects in a Lazy Language
Lecture #21
  ? Tuesday, March 28th
Designing Domain Specific Languages (DSLs)
Side-note: WSJ on the proliferation of PLs
Syntax Transformations: Macros
Macro Problems
Complexity of S-expression transformations
Scoping problems
Lecture #22
  ? Tuesday, April 4th
Scheme (and Racket) Macros
Meta Macros
Lazy Constructions in an Eager Language
Recursive Macros
Another example: a simple loop.
Problems of syntax-rules Macros
Lecture #23
  ? Tuesday, April 4th
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
Macro Conclusions
Side-note: macros in mainstream languages
Lecture #24
  ? Tuesday, April 4th
What is a Type?
Our Types — The Picky Language
Lecture #25
  ? Wednesday, April 5th
Typing control
Extending Picky
Implementing Picky
Lecture #26
  ? Tuesday, April 11th
Implementing Picky (contd.)
Typing Recursion
Extending Picky with recursion
Typing Data
Judgments for recursive types
“Runaway” instances
Lecture #27
  ? Tuesday, April 11th
Type soundness
Explicit polymorphism
Polymorphism in the type description language
Type judgments for explicit polymorphism and execution
Explicit polymorphism conclusions
Web Programming
Basic web programming
Continuations: Web Programming
Simulating web reading
Lecture #28
  ? Tuesday, April 18th
More Web Transformations
Transforming a recursive function
Using sum/k
Converting stateful code
Converting higher order functions
Highlevel Overview on Continuations
An Automatic Continuation Converter
Lecture #29
  ? Tuesday, April 18th
Continuations as a Language Feature
Continuations in Racket
Playing with Continuations
The Ambiguous Operator: amb
Delimited Continuations
Continuation Conclusions
Lecture Notes, single file
  ? Tuesday, April 18th
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