A simple Dart REPL in a Flutter UI.

The usual Flutter compile steps apply:

flutter pub get
flutter run

This project should run on all platforms Flutter runs on.

There's the Flutter package xterm that supplies a fully featured terminal emulator that's even capable of running vim and any other command line tool (when properly hooked up).

There's the Dart package dart_eval that can compile Dart-like code to a bytecode at runtime and execute it.

My thoughts were, what happens when we combine them?

This is the result. I had some trouble getting a readline equivalent working, since without an underlying shell, we actually don't have anything like that and just get keyboard events. The code is based on cli_repl, but since that code assumes that there's dart:io or dart:html behind it, I had to copy the code and adapt it.

• Can execute anything dart_eval can execute.
• Can be extended to expose extra classes via dart_eval.
• Wrote a small wrapper to allow the use of await directly in the command line (without a wrapping async function).
• Basic text editing with arrow keys support (no emacs shortcuts).
• History for 10 entries, can be navigated with arrow up/down.

Unfortunately, dart_eval does not support a lot of Dart features we would benefit from. It does not expose all std functionality (for example, Iterable.generate) and even basic things like ?: and the modulo operator % do not work. However, I hope that this improves over time.

Also, multiline entry isn't supported right now. The text entry code would support it, but it's unclear at the moment how I could determine whether the entry is complete or not.

Further, the output is just converting whatever comes in into a string (via toString). It does not allow object introspection, since this is not possible in Dart. However, the type returned by dart_eval could allow for other options, I haven't looked into this yet.

Finally, the detection whether the entry should be a oneliner (arrow function) is very basic. Right now it just checks whether the last character is not a ;. If I had a full AST of the parsed code, I could implement a better detection (such as checking whether the top level is just a single expression).

The idea behind this package is that this allows embedding a command line into any Flutter application, for example as a console like in the id or Valve games (Doom, Quake, Source Engine, etc). This would enable a very flexible debugging experience, since all kinds of subsystems could be exposed to this. Still, it allows full sandboxing of the environment, if this is desired.

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