Support lists in pattern matches

[pbiggar]

Right now, we don't support lists in pattern matches. We'd like to. They would look like this I imagine:

match myList
  [] -> something
  [a] -> something else
  [1,b] -> another thing
  [a,b]  -> another thing

I'm unclear whether we also want to support head :: rest style, but if so we'll make another issue.

Adding a language feature like this involves several steps:

• add it to the AST (both expr and FluidExpression.t, and the converter between them, if it hasn't been removed by then)
• add serializers between the frontend and the backend/analysis
• add the execution to backend/libexecution/ast.ml
• add "fluid" tokens and keystrokes (in client/src/fluid/fluid.ml) to allow them to be added
• make sure they can be deleted in Fluid.ml as well

Typically a good strategy is to do the frontend component only as a first step, putting it behind a feature flag). The backend component is generally more straightforward. This task is achievable, but it has many steps and isn't small. Definitely doable by a determined contributor.

[StachuDotNet]

I found a duplicate issue #3319. At time of closing that Issue, its contents were:

Pattern matching doesn't support lists yet. We should support:

• [ ] literal lists
• [ ] (multiple) cons

Maybe this Issue focuses on just literal lists, and cons-style matching waits for a separate Issue?

[pbiggar]

Done!