Luna REPL

[iamrecursion]

Summary

As part of our vision for proper interactive editing in Luna, we want to provide a REPL where users can experiment with code and evaluate snippets as part of development. It should be available from the command line, as well as inside Luna Studio (though potentially hidden), and should support some sensible subset of the IDE protocol to allow for a good interactive editing experience. This includes support for easy debugging.

Value

Luna currently lacks functionality to enable a properly interactive editing experience. While we have the live evaluation on the graph in Luna Studio, this is a limited set of actions required of an interactive experience. Implementing a REPL and associated debugging functionality for Luna programs would expand it to be a usable interactive editing experience.

Specification

The design and implementation for the REPL must support the following functionality.

• Embeddable: It must be possible to embed the REPL via sockets (or other methods) inside an editor that has support for terminal buffers.
• Interactive Editing: It should support a relevant subset of the IDE Protocol, including: get type, hole fits, show documentation, get completion, and debugging.
• Highlighting: When in a terminal with support for highlighting, the REPL should use the semantic highlighting from the IDE protocol. It should, however, have the option to operate without colours.
• Debugging: The REPL should support interactive debugging, using the functionality for it exposed by the IDE protocol.

Acceptance Criteria & Test Cases

• Luna has a REPL (luna repl), which supports all of the above functionality.
• The REPL is embeddable without much effort.