A proper type system for Nu

### Related problem We at [Codchi](https://codchi.dev) are currently considering a rewrite from Haskell to Nushell. Coming from Haskell, however, I miss a few things which are crucial for a typed functional language, especially if you want to write more than just a script. Don't get me wrong, Nushell is already an amazing shell, but there are some enhancements that would enable writing larger applications in Nushell. ### Describe the solution you'd like #### Algebraic Datatypes A really useful feature of Rust and Haskell is *Algebraic Datatypes*, a fancy name for records and sum types. The latter is known as `enum` in Rust and is used for `Result`, `Option` and so on. This is one of the Features which set Rust and Haskell apart from more mainstream languages like Java, Go, C# and so on. Nushell already has `record<...>` and `table<...>`, but lacks a convenient way to define them (see #10630). 🎯 I think an ergonomic solution is to allow multiline record declarations and standalone types, just like `struct` in Rust: ```nushell type foo = record< bar: int, baz: string, my_field: my_custom_type, my_other_field: my_alias ... > type my_custom_type = record<...> type my_alias = decimal ``` On the other hand, Nushell lacks sum types. The syntax could look like this: ```nushell type my_sumtype = enum< variant_a: int, variant_b: record<foo: string, bar: int> > ``` Also they require pattern matching support to force handling *all* possible variants of a

Posted by htngr on Nov 20, 2023, 1:14 PM

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