PL: Resources

Class Notes

These are the class notes files. They are not a substitute for taking your own notes in class, and they certainly cannot compensate for not coming in.

Lecture #1
    Tuesday, September 11th
Intro to CS4400/CS5400
Intro to Programming Languages
Lecture #2
    Tuesday, September 11th
Intro to Racket
Side-note: “Goto Statement Considered Harmful”
Quick Intro to Racket
Lecture #3
    Tuesday, September 18th
Lists & Recursion
Some Style
Tail calls
Note on Types
Side-note: Names are important
Lecture #4
    Tuesday, September 18th
BNF, Grammars, the AE Language
Simple Parsing
Lecture #5
    Tuesday, September 25th
The match Form
Semantics (= Evaluation)
Side-note: Compositionality
Implementing an Evaluator
Implementing The AE Language
Intro to Typed Racket
Bindings & Substitution
WAE: Adding Bindings to AE
Evaluation of with
Lecture #6
    Tuesday, September 25th
Evaluation of with (contd.)
Formal Specs
Lazy vs Eager Evaluation
de Bruijn Indexes
Lecture #7
    Tuesday, October 2nd
Functions & Function Values
Implementing First Class Functions
The FLANG Language
Introducing Racket’s lambda
Using Functions as Objects
Using Higher-Order & Anonymous Functions
Lecture #8
    Tuesday, October 2nd
Side-note: “Point-Free” combinators
This is not Runtime Code Generation
Substitution Caches
Implementation of Cache Functionality
Formal Rules for Cached Substitutions
Evaluating with Substitution Caches
Lecture #9
    Tuesday, October 9th
Dynamic and Lexical Scopes
Dynamic versus Lexical Scope
Lecture #10
    Tuesday, October 9th
Implementing Lexical Scope: Closures and Environments
Fixing an Overlooked Bug
Lexical Scope using Racket Closures
More Closures (on both levels)
Types of Evaluators
Feature Embedding
Lecture #11
    Tuesday, October 16th
Recursion, Recursion, Recursion
Recursion without the Magic
The Core of make-recursive
Denotational Explanation of Recursion
The Y Combinator
The main property of Y
Yet another explanation for Y
Lecture #12
    Tuesday, October 16th
Typing the Y Combinator
Lambda Calculus — Schlac
Church Numerals
More Encodings
Lecture #13
    Tuesday, October 23rd
Alternative Church Encoding
Recursive Environments
Recursion: Racket’s letrec
Lecture #14
    Tuesday, October 23rd
Implementing Recursion using letrec
Implementing rec Using Cyclic Structures
Boxes and Mutation
Lecture #15
    Tuesday, October 30th
Types for Boxes
Boxof’s Lack of Subtyping
Implementing a Circular Environment
Lecture #16
    Tuesday, October 30th
Variable Mutation
State and Environments
Implementing Objects with State
The Toy Language
Lecture #17
    Tuesday, November 6th
Compilation and Partial Evaluation
Lecture #18
    Tuesday, November 6th
Lazy Evaluation: Using a Lazy Racket
Lazy Evaluation: Some Issues
Lazy Evaluation: Shell Examples
Lecture #19
    Tuesday, November 13th
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)
Sloth: A Lazy Evaluator
Getting more from Sloth
Implementing Call by Need
Side Effects in a Lazy Language
Lecture #20
    Tuesday, November 13th
Designing Domain Specific Languages (DSLs)
Side-note: WSJ on the proliferation of PLs
Syntax Transformations: Macros
Macro Problems
Complexity of S-expression transformations
Lecture #21
    Tuesday, November 20th
Scoping problems
Scheme (and Racket) Macros
Meta Macros
Lazy Constructions in an Eager Language
Recursive Macros
Another example: a simple loop.
Lecture #22
    Tuesday, November 20th
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, November 27th
Macro Conclusions
Side-note: macros in mainstream languages
What is a Type?
Our Types — The Picky Language
Typing control
Extending Picky
Lecture #24
    Tuesday, November 27th
Implementing Picky
Lecture #25
    Wednesday, November 28th
Typing Recursion
Extending Picky with recursion
Typing Data
Lecture #26
    Thursday, November 29th
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 #27
    Tuesday, December 4th
Web Programming
Basic web programming
Continuations: Web Programming
Simulating web reading
More Web Transformations
Transforming a recursive function
Using sum/k
Converting stateful code
Converting higher order functions
Highlevel Overview on Continuations
Lecture #28
    Tuesday, December 4th
An Automatic Continuation Converter
Continuations as a Language Feature
Continuations in Racket
Playing with Continuations
Lecture #29
    Wednesday, December 5th
The Ambiguous Operator: amb
Delimited Continuations
Continuation Conclusions
Lecture Notes, single file
    Wednesday, December 5th
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, start DrRacket, use the “Install .plt File” in the File menu and enter — and restart DrRacket after it is installed. You can also use the “Setup PLT” application to install it if you want to do an off-line installation.

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