Phase 5 cont. Adds `select` statement evaluation:
go-select-try-case env COMM →
:not-ready / extended-env / :eval-error
go-select-pick env CASES DEFAULT-OR-NIL →
body-result / blocked-error
go-eval-select-stmt env STMT — public entry
Walks cases in declared order:
* :send case — always ready in v0 (unbounded buffer). Sends value
via go-chan-send! and returns env unchanged.
* :short-decl / :assign case — RHS expected to be unary <- on a
channel. Ready iff go-chan-len > 0; on success, recv-into-var
binds the new value in env.
* Bare recv (:app (:var "<-") [CHAN]) — ready iff len > 0; consumes
the value (discarded).
* :default — deferred until end of walk. Runs if no other case
ready. Absence + no ready case → (:eval-error :select-blocked-
no-default).
New `go-chan-len` accessor on the channel closure-bundle so the
select can peek without consuming.
Subtle bug fix: the :select stmt branch in go-eval-stmt was returning
the old env instead of the env returned by the case body. Assignments
inside select cases (`select { case <-ch: x = 1 ; default: x = 99 }`)
now stick.
Tests (6):
default fires when no case ready
recv case fires when ready
recv-into-var binds the value
send case always ready
picks first ready case (deterministic order in v0)
no default + nothing ready → blocked error
combined with goroutine fan-in
runtime 18/18, total 475/475.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Phase 5 (goroutines + channels) opens.
lib/go/sched.sx is the **independent implementation** referenced by
plans/lib-guest-scheduler.md — the first-consumer cut whose realised
shape will inform the eventual sister kit.
Channel representation:
(list :go-chan SEND-FN RECV-FN CLOSED?-FN CLOSE!-FN)
Each closure shares a mutable `buf` (a list mutated via append! and
set!) and a `closed` flag. Channel identity is closure-instance —
two `make()` calls produce distinct values per Go spec § Channel types.
Primitive API in sched.sx:
go-make-chan / go-chan? / go-chan-send! / go-chan-recv! /
go-chan-closed? / go-chan-close!
Eval integration in eval.sx:
* `make` and `close` added as builtins. v0 `make()` takes no args
and returns an unbounded-buffer channel.
* `:send` stmt → go-chan-send! on the channel.
* Unary `<-` recv on channel values → go-chan-recv!. `:empty`
sentinel converted to nil (stand-in for blocking semantics).
* `:go expr` → synchronous eval (v0 limitation, see sched.sx
header).
**v0 concurrency model — synchronous goroutines.** SX doesn't expose
first-class continuations to guest code, so v0 runs `go f()`
immediately and depends on the spawned goroutine running to
completion before the main goroutine receives. This is the right
semantics for the simple producer/consumer patterns covered here.
True preemption with blocking send/recv is Phase 5b — requires either
a CEK-style trampolining eval rewrite or kit-level continuation
support. Logged in sched.sx header and in the sister-plan diary.
Runtime suite (12 tests):
* 6 direct API tests: identity, FIFO order, closed-flag
* 6 source-level: make + send + recv, go ping-pong, close,
multi-goroutine fan-in, worker-with-result
Sister-plan scheduler diary updated with the channel-as-closure-
bundle insight and the v0 synchronous-spawn caveat.
runtime 12/12, total 469/469.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
