kmicinski

#lang racket

;; CIS352 'S26 Lecture Notes -- Introduction to the Untyped λ-Calculus 

;; ☐ The Untyped λ-Calculus
;; ☐ β-reduction
;; ☐ λ-calculus Semantics and Normal Forms

;; Today we will learn about one of the most central aspects of the
;; course: Alonzo Church's untyped λ-calculus. The λ-calculus is not

kmicinski

#lang racket

;; CIS352 -- Feb 24, 2026

;; □ -- Sets in Racket

;; QuickAnswer

(set) ;; empty set 
(set 1 2 3) ;; {1, 2, 3} = {3, 2, 1} = {3, 3, 2, 2, 1, 1, 1}

kmicinski

#lang racket

;; CIS352 -- Feb 18, 2026

;; Consider watching this lecture video on foldr:
;; https://www.youtube.com/watch?v=WUAI_v110NQ&list=PLXaqTeMx01E_eK1ZEpKvKL5KwSaj7cJW9&index=15

(define (count-evens? l)
  (foldr (lambda (next-elt acc) (if (even? next-elt) (+ 1 acc) acc))
         0

kmicinski

#lang racket
;; CIS352 -- Practice on Pattern Matching
;; 
;; If you want more practice, I have a video here: https://www.youtube.com/watch?v=RJFkmh9Wo8o

(define (filter f l)
  (if (empty? l)
      '()
      (cons (f (first l)) (filter f (rest l)))))

kmicinski

#lang racket

;; CIS352 -- Spring 2026

;; Today's agenda...
;; □ -- Evaluation Order
;; □ -- Printf-style debugging and reachability hypotheses
;; □ -- Evaluation of function call
;; □ -- The Stack
;; □ -- Tail Position and Tail Calls

kmicinski

#lang racket

;; CIS352 -- The Algebra of Programming
;; Spring 2026 -- Kristopher Micinski

;; Introduction:
;; 
;; Students often ask (in CIS352): "why learn Racket, a language with
;; an arcane syntax that I might not use outside of this class?" It is
;; a very reasonable question, and today we will answer it directly:

kmicinski

#lang racket
;; CIS352 -- Feb 3, 2026

;; Pattern matching:
;; □ -- Trees, manually
;; □ -- Recursion over trees
;; □ -- Introducing pattern matching
;; □ -- Matching list patterns ("quasipatterns")
;; □ -- Matching predicate patterns
;; □ -- Trees, and algebraic data types generally

kmicinski

#lang racket

;; CIS 352 -- Spring 2026
;; 1/27/26 (I believe)

;; quickanswer.harp-lab.com

;; the define form lets us define funcitons
;; (define (f x y z) e-body)
(define (both-even? n0 n1)

kmicinski

#lang racket

;; Notes, 1/22
;; f is a function from α → bool (i.e., a predicate)
;; l is list of αs
;; we return the number of elements in l such that
;; they satisfy the predicate f

;; (count even? '(0 1 2 3 4)) ;; => 3
#;(define (count f l)

kmicinski

#lang racket

;; CIS352 'S26 -- 1/29 through 2/3

;; □ -- More practice with lambdas
;; □ -- Mapping
;; □ -- Explaining recursion and why it matters
;; □ -- Our first non-list recursive type: trees
;; □ -- Pattern matching