russell@unturf.com 574ddc50d7 S-expressions over sockets — RPC + remote REPL in portable Scheme ...

Fuses portal (Scheme-source-as-interchange) with sockets (bytes over
the network). Wire protocol: one S-expression per connection. Same
server + client .lsp runs byte-identically in Python, C, and asm.

New primitives in all three impls:
- read-from-string — parse one sexp from a string

Asm gets two more:
- symbol->string — standard R7RS, was missing
- eval — evaluate a Scheme value in the global env (Python + C had
  it as a special form; asm exposes it as a builtin)

examples/rpc-server.lsp (port 9080):
- Whitelisted dispatch: ping / add / mul / fib / echo
- Never calls eval on client input; safe by construction
- Uses heap-snapshot/restore for O(1) memory on asm
- ~90 lines, portable

examples/rpc-client.lsp:
- Sends one request, reads one response, displays both
- 45 lines, portable

examples/repl-server.lsp (port 9081):
- DANGER: full remote eval. Any Scheme form accepted and evaluated
  in the server's global env. Persistent across connections.
- Deliberately does NOT use heap-snapshot — remote (define x ...)
  lives in the global env above any snapshot point; rewinding would
  invalidate the new binding. The ulimit -v 512 MB safety net
  (documented in CLAUDE.md) ensures an escaped process can't crash
  the machine.
- ~70 lines, portable. Demonstrates what "the language IS the
  interchange format" gets you at the limit: a single socket and
  a single primitive (eval) carry a full-powered REPL.

Verified 3×3 server×client matrix: all 9 combinations green.
All 132 asm + 571 py + 189 shared + 83 c tests still pass.

One quirk discovered and worked around: in asm, a closure captures
its env chain by pointer at define time. Forward-referenced names
in mutually-recursive toplevel defines can fail under specific
heap-restore patterns — see the leaf-first ordering note in
rpc-server.lsp.

2026-04-17 09:00:04 -04:00

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