SPLV20 Alternatives

SPLV20 reviews and mentions

• The Little Typer – The Beauty of Dependent Type Systems, One Step at a Time
  4 projects | news.ycombinator.com | 11 Oct 2022

  Internally, the Idris2 compiler uses deBruijn numbering for its terms, which is tricky to get right once you start trying to manipulate terms. To help with this, it keeps a list of the names corresponding to the deBruijn indices at the type level. The type checker catches mistakes as you write code to manipulate them (inserting names, removing names, or renaming things).

  I ran through some exercises teaching this technique[1]. My take-away as a beginner was that it was a pain to make the compiler happy and my code that the compiler didn't like was actually wrong.

  I remember reading someone had written a functional red-black tree (with proof of correctness leveraging dependent types) and said the delete algorithm naturally followed from the types. That has was not my experience (delete wasn't immediately obvious to me), but I need to find some time to give it another go.

  The Idris2 docs have an example of a lambda expression interpreter[2] whose terms have a vector of the types in the environment as a type parameter (erased at runtime), to ensure everything is type safe in the resulting interpreter.

  Typescript has added some bits of dependent typing. For example, asserting a function returns true if the argument has type X, that a function throws if the argument is falsy, and I think type level string manipulation. They are fairly pragmatic, it's not a research language, so I presume that specific functionality is useful to a lot of people. I've used it a little bit of it to help the type checker infer non-null after my assert function was called.

  All of that said, I think people are still exploring how dependent types can be used in practice.

  [1]: https://github.com/edwinb/SPLV20/blob/master/Code/Lecture2/E...