Implement the following plan:

Fix #85: Support receive into indexed target variables

Context

Channel receive (ch ? var) only accepts a simple identifier as the target. Indexed targets like flags[0] or state.of.neighbour[d] cause parse failures because the parser uses expectPeek(IDENT) and leaves the [...] unprocessed. The same limitation affects ALT case parsing. This blocks historical-examples/life.occ (issue #72).

The fix adds VariableIndices []Expression to Receive and AltCase, mirroring the existing ChannelIndices and Assignment.Indices patterns.

Changes

1. AST — `ast/ast.go`

Add VariableIndices []Expression field to both structs:

Receive (line 378): Add after Variable string
AltCase (line 402): Add after Variable string

2. Parser — `parser/parser.go`

After each expectPeek(IDENT) + Variable = curToken.Literal site, add index collection loop:

for p.peekTokenIs(lexer.LBRACKET) {
    p.nextToken() // move to [
    p.nextToken() // move past [
    <target>.VariableIndices = append(<target>.VariableIndices, p.parseExpression(LOWEST))
    if !p.expectPeek(lexer.RBRACKET) {
        return nil
    }
}

5 locations: 1. parseReceive() (~line 1294) — stmt.VariableIndices 2. parseIndexedOperation() receive branch (~line 792) — stmt.VariableIndices 3. parseAltCase() simple channel (~line 1765) — altCase.VariableIndices 4. parseAltCase() indexed channel (~line 1785) — altCase.VariableIndices 5. parseAltCase() guarded channel (~line 1825) — altCase.VariableIndices

3. Codegen — `codegen/codegen.go`

Build variable reference with indices using existing generateIndicesStr():

6 locations: 1. generateReceive() simple path (~line 1362): Append indices to varRef 2. generateReceive() sequential path (~line 1349): Append indices to primary varRef 3. generateAltBlock() guarded case (line 1906): Build varRef with indices 4. generateAltBlock() indexed channel case (line 1908): Build varRef with indices 5. generateAltBlock() simple channel case (line 1912): Build varRef with indices 6. generateReplicatedAlt() (line 2043): Build varRef with indices

Pattern at each site:

varRef := goIdent(name)
if len(indices) > 0 {
    varRef += g.generateIndicesStr(indices)
}

4. Tests

Parser tests (parser/parser_test.go): - TestReceiveIndexedVariable: ch ? flags[0] — verify VariableIndices has 1 entry - TestReceiveMultiIndexedVariable: ch ? grid[i][j] — verify 2 indices - TestIndexedChannelReceiveIndexedVariable: cs[0] ? flags[1] — both channel and variable indexed

E2E tests (codegen/e2e_concurrency_test.go): - TestE2E_ReceiveIntoIndexedVariable: Simple channel receive into array element - TestE2E_IndexedChannelReceiveIntoIndexedVariable: cs[i] ? arr[j] pattern

Verification

go test ./...

If you need specific details from before exiting plan mode (like exact code snippets, error messages, or content you generated), read the full transcript at: /home/david/.claude/projects/-home-david-projects-code-associates-occam2go/cccd5ad5-122e-445d-bd16-94c2d59c7a1a.jsonl

15 read · 13 edit · 8 taskupdate · 7 grep · 4 taskcreate · 3 bash

All done. Here's a summary of the changes:

AST (ast/ast.go): Added VariableIndices []Expression to both Receive and AltCase structs.

Parser (parser/parser.go): Added index collection loops (for p.peekTokenIs(lexer.LBRACKET)) after every Variable = p.curToken.Literal site — 5 locations across parseReceive(), parseIndexedOperation(), and parseAltCase() (simple, indexed-channel, and guarded branches).

Codegen (codegen/codegen.go): At all 6 sites that build varRef from the variable name, added generateIndicesStr() when VariableIndices is non-empty — in generateReceive() (simple + sequential paths), generateAltBlock() (guarded, indexed-channel, and simple-channel branches), and generateReplicatedAlt().

Tests: 3 parser tests (TestReceiveIndexedVariable, TestReceiveMultiIndexedVariable, TestIndexedChannelReceiveIndexedVariable) and 2 e2e tests (TestE2E_ReceiveIntoIndexedVariable, TestE2E_IndexedChannelReceiveIntoIndexedVariable).

All tests pass including the course module vet check.

Claude Code transcript