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agent: builder model: opus max_turns: 150 budget_usd: 40 —

Brief: a grammar rule and entry that take type parameters (entry rule read[T] -> T, ADR-grammar-2 D1, #1019 step 1)

Score: owner’s direction (2026-10-31, “bauen ja”): #1019 (json::read[T] through a grammar) is the next tools step; its blockers (#859 steps 1-4, D11) are built (0.0.1317-0.0.1321). S=A, O=~3M tokens, C=~2M tokens, grammar checker/emitter.

Problem (probe it with target/fast/nikaia check at your start)

A program-local grammar whose rule takes a type:

grammar Num {
    entry rule read[T] -> T = v:Digits[T] eof -> { v }
    rule Digits[T] -> T = d:text([0-9]+) -> { T::parse(d) }   // or whatever action the existing grammar tests use to build a value of T
}
fn main() { let n = Num::read[i64]("42") … }

Expected today: a parse error or NK1230 at [T]. Confirm and say what you found; adapt the action to a form the checker already accepts (a match T::kind is step 2, not yours - pick a body where T only appears in the return type and in calls handing it on, e.g. Wrap[T] returning T from a sub-rule called with [T]).

Decision (accepted records, no owner decision needed)

Locations

To build

  1. Type parameters on a rule and an entry of a program-local grammar, with the substitution per list of type arguments and one emitted copy per list, the call G::entry[T](input) from code, the hand-on Rule[T] inside a pattern, a bound, and NK1230 for a value in the brackets. Tests in tests/compiler/tests/: grammar_a_rule_takes_a_type.nika + .stdout (two types through one entry, both copies used), grammar_a_value_where_a_rule_takes_a_type_is_refused.nika + .stderr (NK1230). Commit grammar: a rule and an entry take type parameters (ADR-grammar-2 D1), Part of #1019.

Done when

The new tests pass through nikaia test --project tests/compiler; each failed once against the compiler without your change (say so under Tests:); the existing grammar_* tests still pass (run that subset by name); lower-std fixpoint clean; cargo build --profile fast -p nikaia; the cheap checks of Rules. Changelog: one line.

Stop and report if

match T::kind in a rule body is needed (step 2, brief j2); members[S] (step 3); an edit outside the parser, the AST, check_*.nika, emit_*.nika, grammar_*.nika, grammar_run.rs, their lowered files and the new tests; a form beyond ADR-grammar-2; an error in another agent’s file. Another session works on moving grammar_run.rs into Nikaia (GR): if git log shows a fresh commit there, rebase-free coexistence matters - say so under Found:.

Not yours, never stage: every file git status shows modified or untracked at your start, and every docs/briefs/* file except your report.

Rules (CLAUDE.md; this block is pasted into every brief, also a fix-forward)

Report (at most 15 lines, to exactly /home/user/Nikaia/docs/briefs/tools/j1-1019-rule-type-parameters.md.report.md)

Fields of docs/architect.md, Briefs and reports: Result: done|noop|partial|blocked (the bare word alone on that line: Result: done, never a summary after it, which cuts the batch, b869a 2026-10-27; Owner: is a question for the owner or none, never a role), Files, Commit, Body (optional, one paragraph for the commit message), Fixes, Pushed, Tests, Gate (green|red), Deviation, Found, Needs, Changelog, Owner, Disk freed, and for a move Rs2nika: (the kept N of M lines of rs2nika --score, then the three costliest hand edits; none for a task that moves no Rust, none (redesign) for a brief with Shape: redesign and no Convert: line). none where nothing, and then the bare word: Deviation: none (a note) cuts the batch (batch.nika compares exactly); a note goes into the commit message. Found: is only for a defect outside your change (it cuts the batch); a process event such as another session resetting or rewriting your files is no Found:, it goes under Needs: (m3a 2026-10-28); a converter draft that came out wrong is no Found:, it is one of the costliest edits under Rs2nika:, which the converter lane reads (e12-4b 2026-10-27); how you solved your own step goes into the commit message. Deviation: is only a step of the brief built otherwise than written or not built (a choice the brief left to you, such as keep what X needs and say so, is no deviation: it goes into the commit message; nor is building two steps in one commit when every step is built, e12-3a 2026-10-27, nor a step another commit on develop already built, shown by your test failing with that commit’s change reverted, b889 2026-10-27: name the commit in Body:, nor a test’s expected .stdout/.stderr taken from what the program really prints where the brief’s sketch of it was short or wrong, b934 2026-10-29: say so in Body:, nor a lowering that follows the ADR governing it where the brief’s expected lowering contradicts that ADR, b933 2026-10-29: name the ADR in Body:, nor a lowering other than the brief’s where rustc cannot take the brief’s, b1029 2026-10-31: say why in Body:, nor re-keying an allow-list entry (KNOWN) whose hash changed for the same program and the same reason, b-fixforward-sweep2 2026-10-28: say so in Body:, nor an existing test’s expected .stdout/.stderr updated because your change rightly changes the message it prints, b1012b 2026-10-31: name the test in Body:); how you verified (e.g. a test not run against the unfixed compiler) goes under Tests:. A noop says why under Tests: (what was probed), not under Deviation:. Final answer, one line: done <sha>, report <path> (or BLOCKED: ... / PUSH REJECTED ...).

Attribution: Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com Claude-Session: https://claude.ai/code/session_01UVxJDvLe1uS47UcqA9y1U2

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