seabbs Julia REPL over MCP
The mcp__julia-repl__* tools drive a Julia process that stays alive for the
whole session, so startup and compilation cost is paid once rather than on every
julia -e.
dotfiles/claude/settings.json starts the server and
dotfiles/julia/setup-packages.jl installs it into the @AgentREPL shared
environment.
Invoking it
| Tool | Use |
|---|---|
eval |
run code (code) |
revise |
reload edited files (action="revise") |
info |
Julia version, active project, worker pid, user variables |
activate |
switch project (path), then pkg action="instantiate" |
pkg |
add, rm, status, update, test, develop |
session |
isolated named sessions (action, name) |
reset |
kill the worker and spawn a clean one |
The server activates the session's working directory on startup, so in a package
repo the package is already the active project.
log_viewer opens a terminal in the human's tmux, so ask before calling it.
Hot or cold
Iterate hot, verify cold.
Reach for a fresh process, either reset or plain julia --project=. in Bash,
when:
- verifying anything before a commit, so no result rests on session state
- measuring startup, TTFX, or precompilation
- a reload leaves behaviour that no longer makes sense
Everything else belongs in the warm session.
Revise
Call revise with action="revise" after editing a .jl file, then re-eval.
Method changes reload, and on Julia 1.12 struct and const changes reload too,
verified here with Revise 3.16 and the revise_structs preference that
setup-packages.jl sets.
reset remains the fix when a reload leaves the session inconsistent.
A script outside a package needs revise with action="includet" once.
Tests
Narrow the filter while iterating, then run the full suite in a fresh process before finishing.
@run_package_tests filter = ti -> contains(ti.filename, "growth")
@run_package_tests filter = ti -> ti.name == "growth rate stays positive"
@run_package_tests filter = ti -> :integration in ti.tags
pkg with action="test" is the cold run, since Pkg.test starts its own
process.
One worker per client
The server speaks STDIO and spawns a private worker per client, so Claude Code, pi and Neovim each get their own session and cannot share one. The human tmux and vim-slime REPL is separate again, and stays that way.
Each client costs about 1 GB resident before any package loads (measured: 581 MB
server plus 428 MB worker), so on a shared host drop sessions you no longer need
with session action="destroy".