Type systems are designed to be helpful.
They manage complexity and provide documentation about our code.
Most importantly they provide guarantees about a program. A single complete program.

However, most type systems fall short of providing guarantees beyond a single program.
They do not guarantee that our client can talk to our server.
Nothing is guaranteed when rolling out the latest deployment into a running system.

But can type systems do more?
Can we type check a program without seeing the whole thing?
Can we provide guarantees that a code upgrade will continue to work in a running system?

This talk will take a tour through various languages and their type systems.
We will pass by Fsharp Type Providers, Ocaml 5.0's effect system and Unisons code store.
By the end we will demonstrate how our type systems can give us guarantees about our systems that hold from client to server, and from one version of our software to the next.