Worksheet Mode - Implementation details

In brief, the worksheets extend the Language Server Protocol and rely on the Dotty REPL to evaluate code.


Each of the individual expressions and statements of the worksheet is extracted and passed to the Dotty REPL. After the REPL has finished evaluating one unit of input, it emits a special delimiter that indicates the end of the output for this input. (See

This process continues until all input has been evaluated.

The Dotty REPL is run in a separate JVM. The Evaluator (see will re-use a JVM if the configuration of the project hasn't changed.

Communication with the client

The worksheets extend the Language Server Protocol and add one request and one notification.

Run worksheet request

The worksheet run request is sent from the client to the server to request that the server runs a given worksheet and streams the result.



Worksheet output notification

The worksheet output notification is sent from the server to the client to indicate that worksheet execution has produced some output.