Class Tu/Th 1:25 - 2:45 p.m. in PH A18C

Recitation F 1:25 - 2:15 p.m.. in GHC 4102

Fall 2021

12 units

**Jonathan Aldrich**

aldrich at cs dot cmu dot edu

TCS 422

Office hours: Thursday 5-6pm in TCS 422, or by appointment

For appointments outside of office hours, email the instructor.

TA Sam Estep

samueles at andrew

Office hours: Tuesday 3-4pm in TCS 310

## Course Description

This course provides a broad and pragmatic foundation in the most basic tool of the programmer: programming languages. It starts with the fundamentals of syntax, parsing, and binding, the core structural concepts in programming languages. The course will then cover program semantics and type systems, and students will learn to relate them with a type soundness theorem. Finally, a coverage of intermediate optimization and code generation offers the opportunity to discuss both producing efficient code and reasoning about the correctness of program transformations. Assignments involve a combination of tool-assisted formal reasoning and proofs about programming languages, and implementing these language constructs in a compiler.

**Prerequisites.**
Programming maturity and knowledge of reasoning about programs equivalent to passing 15-150, and mathematical maturity equivalent to passing either 15-251 or 21-228).
Students with substantial math and programming experience who have not satisfied the specific prerequisites can contact the instructor for permission to enroll.

**Requirements Satisfied.**This course fulfills the **Logic and Languages constrained elective category** for the Computer Science major.

### Why take this course?

**Programming Languages and Compilers are fundamental to programming, and you can learn about both in one course.**By understanding the semantics of languages, you become a better programmer. After understanding how languages are compiled, you will be able to use them better. And it's not unlikely that you'll need to design a little language yourself someday--a scripting language or configuration for your application, for example--so it's good to know how to do it well!**Learn the theory of languages, with the help of an educational tool.**Programming language semantics and type theory is beautiful and fundamental not only to programming but even to the foundations of mathematics. While it sometimes has a reputation for being inaccessible, I've designed a tool called SASyLF that is easy to use and helps you get your proofs right. It's been used successfully at several universities--students like it and we believe it helps make these topics easier and more rewarding!**Our pragmatic approach positions language and compiler concepts in the setting of industrial languages.**We'll cover foundational ideas like the lambda calculus, but we understand that many students want to apply those ideas to languages familiar to them. This course will focus on covering fundamental ideas as they come up in widely-used languages, both making the ideas concrete and also ensuring that what you learn is relevant to your career as a computer scientist or software developer.

### How does this course compare to CMU's other PL/compilers courses?

First of all, CMU has an amazing selection of courses in this area-you can't go wrong! But this course has some differences that make it a particularly great match for some students:

- Compared to 15-312 Foundations of Programming Languages, this course includes the use of a proof assistant (SASyLF), and takes as its point of departure JavaScript (and its typed extension, TypeScript) rather than Standard ML. It gives up some depth specifically on type theory but in exchange includes more content on compilers.
- Compared to 15-411 Compiler Design, this course involves less programming and more proofs (this is true of all Logic and Languages courses, since learning about rigorous proofs is one of the goals of the category). It gives up some depth specifically on compilation, but in exchange includes more programming language and type system content. And don't worry, half of the assignments are programming-you'll still build a compiler!

### Course Syllabus and Policies

The syllabus covers course learning objectives, supplemental textbooks, assessments, late work policy, and policies.## Schedule

Date | Topic and Slides | Additional Reading or Code | Assignments Due |
---|---|---|---|

Aug 31 | Course introduction | PLP, chapter 1 | |

Sep 2 | Syntax and Lexical Analysis | PLP, chapter 2 through 2.2; in-class exercise | |

Sep 3 | RecitationImplementing lexical analysis | ||

Sep 7 | Binding | PLP, chapter 3; in-class exercise | |

Sep 9 | Inductive definitions and proofs | lecture4-induction.txt; in-class exercise | HW1: Lexical analysis |

Sep 10 | RecitationThe SASyLF Proof Assistant | ||

Sep 14 | Dynamic semantics: Big-step | lecture5-dynamics.txt; in-class exercise | |

Sep 16 | Dynamic semantics: Small-step | lecture06-small-step.pdf; in-class exercise | HW2: Inductive proofs |

Sep 17 | RecitationDynamic semantics practice | ||

Sep 21 | Top-Down Parsing | PLP section 2.3; in-class exercise | |

Sep 23 | Bottom-Up Parsing | in-class exercise and reference sheet | HW3: Dynamic Semantics |

Sep 24 | RecitationParsing implementation | ||

Sep 28 | Typing rules | lecture09-typing.pdf; in-class exercise | |

Sep 30 | Type Soundness - Progress | lecture10-soundness.pdf; in-class exercise | |

Oct 1 | RecitationMidterm review | ||

Oct 5 | Type Soundness - Preservation | (same notes as before); in-class exercise | |

Oct 7 | Environmental Semantics | see Big-Step notes, above; interpreter-code.zip; in-class exercise | HW4: Parsing |

Oct 8 | RecitationStatic semantics practice | ||

Oct 12 | Mid-semester exam 1 | ||

Oct 14 | No class | ||

Oct 15 | RecitationSoundness proofs | ||

Oct 19 | Typechecking the Core of TypeScript | notes/lecture13-subtyping.txt | HW5: Static semantics |

Oct 21 | Human Aspects of Language Design | ||

Oct 22 | RecitationImplementing typecheckers | ||

Oct 26 | Code generation | lecture15-webassembly.txt | HW6: Typechecking |

Oct 28 | Intermediate representation | lecture16-ir.txt | |

Oct 29 | Recitation | ||

Nov 2 | Local Optimization | in-class exercise | |

Nov 4 | Global Optimization and Correctness | lecture18-optimization.pdf; in-class exercise | HW7: Code generation |

Nov 5 | No Recitation | ||

Nov 9 | Object-Oriented Programming Concepts and Implementation | lecture19-objects.txt | |

Nov 11 | Garbage collection | lecture20-gc.txt | HW8: Translation correctness |

Nov 12 | RecitationProject discussion | ||

Nov 16 | Register allocation, instruction scheduling, and loop optimizations | lecture21-backend-opt.txt | Project Proposal |

Nov 18 | The Curry-Howard Isomorphism | see Frank Pfenning's excellent lecture notes | |

Nov 19 | Recitation2nd midterm review | ||

Nov 23 | Midterm exam 2 | ||

Nov 25 | No class | ||

Nov 26 | No Recitation | ||

Nov 30 | Register allocation | ||

Dec 2 | Programming languages and compilers research | ||

Dec 3 | Recitation2nd midterm post-review | ||

Dec 7 8:30-11:30am | Project presentations in HH B131 | Project presentations and final deliverables |