Programming Languages — Recitations (Fall 2026)

Each handout is a single .rkt file you open in DrRacket and Run. Running it executes the code, including the tests.

From recitation 3 on, most handouts are written in #lang plai-typed. These are plain Racket files with comments, so you read them in the editor.

A few untyped handouts (recitations 1, 2, 3b, 7, and the macro handout in 5) are Scribble literate programs (#lang scribble/lp2). For these, the Scribble HTML/PDF button also renders the handout as a page with clickable links to the Racket docs.

Recitation 4 also has a Lean 4 file, rec04/bexp.lean. See Setup for how to open it.

Schedule

#	Topic	Handout	Solutions
1	Functional programming in Racket, DrRacket, recursion, lists & higher-order functions	recitation1.rkt	recitation1-solutions.rkt
2	Boolean expressions: structs, writing an interpreter, and optimizations	recitation2.rkt	recitation2-solutions.rkt
3a	Typed boolean expressions in plai-typed: define-type, type-case, exhaustiveness	recitation3a.rkt	recitation3a-solutions.rkt
3b	Pattern matching: literals, wildcards, and destructuring lists	recitation3b.rkt	recitation3b-solutions.rkt
4	Adding pattern matching to the interpreter; boolean expressions and proofs in Lean	recitation4.rkt, bexp.lean	recitation4-solutions.rkt
5	Environments as functions; static vs. dynamic scope	recitation5.rkt, macro.rkt, unhygienic.c	recitation5-solutions.rkt
6	Mutable state: boxes, the store, set!; tables as a language feature	recitation6.rkt, arb.c, ltr.rkt, rtl.ml	recitation6-solutions.rkt
7	Recursion: tying the knot with boxes; the Y and Z combinators; rec via Z	recitation7.rkt, recitation7-interp.rkt	recitation7-solutions.rkt, recitation7-interp-solutions.rkt

How these files work

• Handouts are posted before recitation with exercises left as 'TODO. We fill them in together during the session, so bring a laptop with DrRacket if you want to code along.
• Solutions are posted after recitation as a separate file.

Layout convention:

recNN/
  recitationN.rkt            # handout (exercises as 'TODO)
  recitationN-solutions.rkt  # posted after recitation

Some weeks are split into parts (recitationNa.rkt, recitationNb.rkt, each with its own solutions file).

Setup

1. Install Racket (DrRacket ships with it).
2. Open the handout in DrRacket, e.g. rec01/recitation1.rkt.
3. Press Run. You should see "Hello, world!" in the interactions pane — then you're set.
4. From recitation 3 on, you'll also need plai-typed. In DrRacket, go to File → Install Package… and enter plai-typed, or run raco pkg install plai-typed. To check it worked, open rec03/recitation3a.rkt and press Run. If you see test failures that say TODO, you're set. If you see collection not found, the package isn't installed.
5. For the Lean file in recitation 4, you don't need to install anything. Open live.lean-lang.org in your browser and paste in the contents of rec04/bexp.lean. The panel on the right shows the output of #eval and the proof state as you move your cursor through the file.