Phase 9.1. Channels

Field	Value
MEP	MEP-54
Status	LANDED (on worktree-mep54-impl, not yet merged to main)
Started	2026-05-29 (GMT+7)
Landed	2026-05-29 14:42 (GMT+7)
Tracking PR	#22623
Commit	6c8caa8f52

Gate

8 fixtures: chan_int (cap 1, send 42, recv, print), chan_bool (cap 2, true / false), chan_string (cap 2, hello / world), chan_float (cap 2, 1.5 / 2.25), chan_multi (cap 3, 10 / 20 / 30), chan_five (cap 5, 1 through 5), chan_interleave (mixed send / recv against half-full channel), chan_loop_send (while loop driving send + recv pairs). 269 total transpiler3/go fixtures green.

Lowering decisions

Mochi's bounded ring channel maps directly onto Go's native chan type, so Phase 9.1 emits make(chan T, int(cap)), c <- v, and <-c without any runtime helper. Three aotir nodes dispatch:

• aotir.ChanMakeExpr -> make(chan T, int(cap)). The element type is rendered inline via a gotree.RawExpr{Src: "chan " + elem} so the new chan shape doesn't need a fresh AST node. The capacity expression is lowered first via lowerExpr, then wrapped in an int(...) cast because Mochi's cap is int64 and Go's make wants the machine-width int.
• aotir.ChanSendStmt -> gotree.SendStmt{Chan: ch, Value: val}, rendering as c <- v.
• aotir.ChanRecvExpr -> gotree.UnaryExpr{Op: "<-", X: ch}, rendering as <-c. The Phase 2 UnaryExpr operand-parenthesisation rule handles the case where the receive sits inside another unary expression (-<-c) without emitting the ambiguous --<-c.

TypeChan is added to letTypeText via LetStmt.ChanElemType so var c chan<int> = make_chan(1) gets the right Go annotation. Param and Function do not carry ChanElemType yet, so channels remain locals for now (matching the JVM phase-10 baseline). Lifting channels into function signatures lands in Phase 9.1.1 when a fixture motivates it.

Files changed

File	Purpose
transpiler3/go/lower/types.go	lowerChanType(elem) -> chan Elem
transpiler3/go/lower/expr.go	ChanMakeExpr -> make(chan T, int(cap)); ChanRecvExpr -> <-c
transpiler3/go/lower/stmt.go	ChanSendStmt -> c <- v; letTypeText handles TypeChan
tests/transpiler3/go/fixtures/chan_*/	8 fixtures

Test set

• 8 TestPhase1Hello/chan_* subtests covering scalar element types, capacities 1 / 2 / 3 / 5, half-full interleave, while-loop driven send / recv.

Closeout notes

Phase 9.1 was a small, self-contained patch (3 dispatch arms + 1 type helper) because Go's native chan matches Mochi's semantics almost perfectly: bounded by make capacity, blocking on full send / empty recv. Skipping the runtime helper saves both code size and a per-program initialisation step. Phase 9.2 (streams + subscribers) is the natural sequel, and Phase 9.1.1 (channels as function parameters and returns) is queued behind whichever phase first writes a fixture that needs it.