Lecture 01

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Welcome! Intro to OCaml

Programming Languages

UW CSE 341 - Winter 2021

Welcome! Stoked for this quarter 🥳

10 weeks to learn fundamentals of Programming Languages

• Become better programmers, even in other languages
• Learn to distinguish surface differences from deeper principles
• Develop a systematic methodology for understanding what programs mean
• Pick up some technical jargon to support further study

What is going to happen?

• Bad course summary:
• “Learn OCaml + Racket”
• Better course summary:
• Understand functional programming vs. object-oriented programming
• Understand static types vs. dynamic types

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Today

1. Course mechanics
2. Our first OCaml program

TODO

• Read the course website
• Make sure Zoom works
• Sign in to Gradescope and the Discussion Board
• Set up your programming environment for OCaml

About Me

• PL research spanning diverse topics
• Compilers, verification, floating point, 3D printing, ...
• First-generation college student
• Purdue (IN, BS 2007) → UCSD (CA, PhD 2014) → UW (WA, Prof 2013)
• 8th year on the faculty, 6th time teaching 341
• Running (slowly), reading, vegan cooking, meditation, …
• Coming off a long Greg Egan binge, listening to Elder, exploring the Zettelkasten fad

2021 off to a

rough start 😭

But CSE 341 always brightens my day ☀️

2021 off to a

rough start 😭

TAs

• Andres Paz
• Kenny Wu
• Michael Flanders
• Jennifer Tao
• Kevin Zhu

The Heroes

of CSE 341!

Course Creator

Dan Grossman

• Eminent PL researcher
• Vice Director of the Allen School
• Highly successful Coursera PL course
• Cornering the market on Internet Dad Jokes (@djg98115)

Course Creator

Dan Grossman

• Eminent PL researcher
• Vice Director of the Allen School
• Highly successful Coursera PL course
• Cornering the market on Internet Dad Jokes (@djg98115)

Recent Course Innovator

James Wilcox

• Former UW PhD Student
• Ported 341 to OCaml
• Lots of great new ideas
• Buckle up 😂

Staying in Touch

• Discussion Board (Ed)
• All asynchronous communication should go through Ed
• Use “private threads” to communicate directly with staff
• First time trying this out, hoping vibrant community emerges!
• Lecture, Section, Office Hours
• Show up, ask questions, hang out!
• Please be patient, kind, and helpful 🤝

Lectures

• Recordings: available to the class, but not public
• Take notes! Preferably with pen and paper first 📝
• Interaction is more fun for everybody!
• Grand challenge figuring out how to make things click over Zoom
• Need help from the whole class to the experience good for everyone
• Let us know if you can’t make it to lecture

Section

• Smaller group meetings, presents new material
• Often needed to complete homework assignments
• Will also be recorded, but also not public
• Same attendance policy as lecture
• Let us know if you can’t make it
• Meets this Thursday
• Get to know your TA!

Office Hours

• Schedule and Zoom links on course website
• Feel free to drop in just to chat!
• Would love to meet everyone this quarter 👋

Remote Learning

• Enormous uncontrolled experiment
• Opportunity to try a bunch of new things!
• Not planning on traditional exams, etc.
• We are committed to figuring this out
• Let us know how we can help make this a great 341
• Your health and safety come first

Homework

• Probably ~ seven-ish assignments
• Mostly programming
• Some PL “theory”
• DO discuss with friends and classmates
• DO NOT look at or share any code!

Homework

• Start early! Some problems need sleep.
• Two late days per assignment (strict)
• No homework help on message board during late period
• Challenge problems: for the fun of it
• Poor effort-to-points tradeoff
• Good effort-to-learning tradeoff
• Don’t attempt challenges till everything else is done!

Academic Integrity

• The rules are to help you learn
• Most cheating arises from procrastination followed by panic
• Much better to ask for an extension and more help instead!
• If you do collaborate too closely, explicitly note that in your submission!
• Don’t believe everything online
• And please don’t post your solutions anywhere

Questions about mechanics?

Programming Languages

• Fundamentals: design, implementation, theory, practice
• View fundamentals through OCaml : and Racket ( )
• Learn a lot from seeing the same idea in different guise
• “Travel to see where you’re from.”
• Focus on functional programming (FP)
• Avoid mutation (assignment statements)
• Functions are values

A Whole New World 🧞‍♂️

• New language (OCaml)
• New editor (VS Code, etc.)
• New mode of exploring (REPL)
• New for me too! (at least for teaching 341)
• I have written my fair share of SML, OCaml, Haskell, Coq, etc. over the years though 👴
• Let’s get set up and start learning the workflow
• The sooner the better -- start early on Homework 01!

Mindset

• It’s too easy to forget how mind-bending programming first was
• “When you're thinking about something that you don't understand, you have a terrible, uncomfortable feeling called confusion.”
• Learning new things often means working through confusion, and that’s OK!
• It’s too easy to think everything is a nail and we only need hammers
• “We become what we behold. We shape our tools and then our tools shape us.”
• Learning a diverse set of tools makes us more robust when facing new problems!

Mindset

• “Let go” of everything you know
• We’ll come back around to more mainstream friends like Java eventually!
• Treat OCaml (“ML”) as some new alien game we’re learning to play 👽 🎲
• We’ll describe OCaml systematically, then apply the same approach repeatedly
• Lots of new concepts, but we’ll be able to compare and contrast language more rigorously
• Trying to “translate everything into Java” will hold you back

Syntax + Semantics

• Syntax: how programs are written down
• Roughly “spelling and grammar”
• Semantics: what programs mean
• Type checking : compile time (aka “static”) semantics
• Evaluation : run time (aka “dynamic”) semantics
• Both syntax and semantics matter
• 341’s view ≈ “Semantics give the essence of a PL. Syntax is more about taste.”

To the keyboard!

Defining Variable Binding

let x = e

Syntax:

• Keyword: let
• Variable: x
• Expression: e
• Many forms!
• Defined recursively!

(* static env = ... *)

(* dynamic env = ... *)

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let x = 34

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(* static env = ...; x : int *)

(* dynamic env = ...; x -> 34 *)

Defining Variable Binding

let x = e

Semantics:

• Type checking
• Type check e : t (t is some type)
• Add binding x ↦ t to static environment
• Evaluation
• Evaluate e to a value v
• Add binding x ↦ v to dynamic environment

(* static env = ... *)

(* dynamic env = ... *)

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let x = 34

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(* static env = ...; x : int *)

(* dynamic env = ...; x -> 34 *)

ML Carefully So Far

• A program is just a sequence of bindings
• Typecheck each binding in order
• Using static environment from previous bindings
• Evaluate each binding in order
• Using dynamic environment from previous bindings
• So far, only variable bindings
• More kinds of bindings coming soon!

For Next Time

• Semantics of expressions
• Make sure to get OCaml setup!
• Guide posted on course website later today
• Please help everyone out on the course discussion board