Functional State Machines in Rust: Typestate and Newtype Patterns

Types are puzzles. A good Rustacean will make sure that the pieces fit to make the picture.

That's why in crates where I need to make sure certain functions are called in order, I use a Ticket<T>, where one function returns a Ticket<Func1Done> with the output and the other has to consume it as an input.

The typestate pattern is a specialization of making only valid states representable

This was a talk at the FUNARCH workshop at this year’s ICFP.

Here’s the livestream: https://www.youtube.com/live/c0pw1iVs_Q0?is=hwm2xa4cZOcqF5tW

Well post the individual talks in the following days!

Maybe I am missing something but where is the entire source code?

I use Typestates and Newtypes extensively. The metric that shows Typestate and Newtypes are beneficial is: How many method calls or parameters can be called / used that compile but are not valid use cases. You want to minimise this number. I love having a type state where I can only make 1 or 2 method calls because the state enforces there are only a few parsing / validation / transition methods available. And there is only one valid way to supply the parameters, I cannot use the strings in the wrong location. I only wish we had named parameters like ObjC.

pdf: https://dl.acm.org/doi/pdf/10.1145/3830438.3830958

Could someone compare this to ST in Idris?

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