Building a Typechecker from scratch [1/20] Introduction to Type theory and checking

This is the first lecture from the "Building a Typechecker from scratch" class where we build a static type checker for a full programming language similar to TypeScript, Java, etc.

In this lecture:

- Introduction to Type theory
- Parsing pipeline
- Abstract Syntax Tree (AST)
- Static vs. Dynamic type checker
- Strong vs. Weak typing
- Sound vs. Unsound type system
- Type safety and Memory safety
- Type judgements
- Type Environment, Г
- Type checking vs. Type inference
- Hindley-Milner (HM) | Type constraints
- Eva programming language
- Union types
- Generic types
- Implementation of Number type

#Typechecker #Type_theory #Programming_language

[Bobbias]

Just discovered your channel and this couldn't have come at a better time. I'm working on a compiler right now and I'm just about finished with parsing. Looking forward to this series.

[robertpalovsky]

Finally! Thank you, Dmitry, I've been waiting for the typechecker course. Learned a lot from your other classes.

[JoeHinkle]

Dmitry I love your lectures on interpreters, so I can’t wait to watch this series!

[claytonsurgeon]

Really appreciate the time you put into your videos. I was hoping you'd make a series on types. Your other series were hugely helpful for me

[eilfjhslihgasoirgh]

Another advantage of static type checkers that for some reason isn't mentioned at 5:25 is that it catches some errors already at compile time and not at runtime (e.g., after you've shipped it)

[louisthibault]

Great stuff as usual, Dmitry! I’ll be signing up for this one as soon as I have a bit of time to dedicate to it :)

[magne]

14:06 Can the types here be defined as generics? So that the + operator is defined for any type. (The goal would be to have a single plus operator instead of needing separate operators for different types, like + for numbers and ++ for strings, like in ReScript).

[rexposadas]

Thanks for the videos. Just curious, what app(s) do you use for presenting your content?

[mateuszdrewniak]

What kind of algorithm will your implementation be based on? Is it bidirectional type checking?

[Hicoffeman]

Hi, I don't know anything about math but I'm autistic and gifted, could you tell me the roadmap for Type Systems? and Compiler Design? I'm not able to differentiate these two concepts, even more so when I understand that Type System is an adaptation of Type theory for computer science...

Furthermore, Type equivalence and type inference are topics covered by which of the three?

btw i liked your videos!