Support ALT replicators

[associate-1]

Description

The parser does not support replicated ALT blocks (ALT i = 0 FOR n), analogous to the already-supported replicated SEQ, PAR, and IF constructs.

Syntax

ALT i = 0 FOR n.inputs
  BYTE ch:
  in[i] ? ch
    SEQ
      out ! ch

This creates n.inputs alternatives, each guarded by in[i] ? ch, and selects whichever channel is ready first.

Affected files

• kroc/modules/course/examples/sort_pump.occ (line 184)
• kroc/modules/course/examples/sort_pump_2.occ (line 184)
• kroc/modules/course/examples/sort_inside.occ (line 213)
• kroc/modules/course/examples/sort_inside_2.occ (line 224, 294)
• kroc/modules/course/examples/bar.occ (lines 327, 338, 352)

This is the single most impactful missing feature — it blocks 5 out of 16 example files.

Current error

sort_pump.occ:184: expected indented block after ALT
sort_pump.occ:184: unexpected token: =

The parser sees ALT and expects an indented block of alternatives, but instead finds the replicator syntax i = 0 FOR n.

Proposed Go mapping

// ALT i = 0 FOR n  →  select over dynamically built cases
// Requires reflect.Select for runtime-variable number of cases

Since Go's select requires statically known cases, the replicated ALT will need reflect.Select to build the case list dynamically at runtime:

cases := make([]reflect.SelectCase, n)
for i := 0; i < n; i++ {
    cases[i] = reflect.SelectCase{Dir: reflect.SelectRecv, Chan: reflect.ValueOf(in[i])}
}
chosen, value, _ := reflect.Select(cases)
ch := byte(value.Int())
// ... body using chosen as i

Related

• Course examples: unimplemented features preventing transpilation #43 - Course examples tracking issue