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Kernel system ​

Summary ​

Interactive computational kernel manager providing Fennel REPL and shell execution with ZeroMQ-based communication. 739 lines of Fennel. Kernels are persisted as JSON files, with history tracking and instance lifecycle management.

Motivation ​

Space needed an in-application computation environment that feels native to the spatial workspace. Rather than shell out to an external terminal, kernels provide REPL and shell sessions as first-class application objects with state persistence, history, and communication channels.

Design ​

  • Kernel instances: Each kernel is a named entity with a command (Fennel REPL or shell), working directory, and list of startup input lines. Persisted as JSON in {data-dir}/kernels/.
  • Lifecycle: create allocates a kernel with a UUID and returns the new object via a created signal. run starts the process (Fennel evaluator or shell subprocess). kill terminates it. Kernels auto-save on state changes.
  • Fennel REPL: Uses FennelEvaluator for in-process Fennel code evaluation with result capture.
  • Shell execution: Spawns child processes via process binding, capturing stdout/stderr. Supports stdin input.
  • ZeroMQ communication: Kernels communicate via ZMQ PUB/SUB sockets, allowing kernel-to-kernel data exchange. Each kernel publishes on a dedicated topic.
  • History: Each kernel maintains a history of inputs and outputs. History is persisted alongside kernel config.
  • Signals: Emits created, removed, updated signals. Signal subscribers can react to kernel state changes (e.g., UI updates when kernel output arrives).

Tasks ​

  • [x] Kernel instance create/run/kill lifecycle
  • [x] Fennel REPL evaluation
  • [x] Shell command execution with stdin/stdout/stderr
  • [x] ZMQ PUB/SUB communication between kernels
  • [x] JSON persistence with history
  • [x] Signal emission for state changes