Stop telling the model list.zip exists, then linting it for using it

[alpibrupa]

Benchmark findings that had been sitting uncommitted in a local working copy (3 weeks stale, 8 commits behind). Rescued and rebased onto current main — the 3-way apply was clean.

Two of the four changes are corrections to things we had wrong, not new features.

1. We were the source of the list.zip hallucination

The prompt's stdlib index advertised zip as a std.list function:

| list | `std.list` | map, filter, fold, head, tail, concat, len, zip, reverse | pure |

list.zip does not exist:

$ lex check   # 0.10.6
{"kind":"unknown_field","field":"zip", ...}

We told the model it was real, then added a linter rule scolding it for reaching for it. The row also omitted six functions that do exist — including list.cons and list.range, which the prompt's own code examples use, and list.enumerate, which the new zip hint tells the model to use instead. A model told "use enumerate" had no confirmation enumerate was real.

Every one of the fourteen functions the row now claims was probed against 0.10.6 individually:

map ✓  filter ✓  fold ✓  head ✓  tail ✓  concat ✓  cons ✓
len ✓  is_empty ✓  enumerate ✓  range ✓  reverse ✓  sort_by ✓  par_map ✓

The str row was checked too — it's an incomplete subset, but claims nothing false, so it's left alone.

2. The && hint was wrong about the language

- "parse error: `&&` is not a Lex operator. Use nested `if`: `if a { b } else { false }` for AND..."
+ "parse error: `&&` is not valid Lex. Use `a and b` (Lex keyword). Example: `acc and (x == y)`."

Lex has and/or. The old hint pushed models into needless nesting to avoid an operator that has a perfectly good keyword equivalent. || gets the same fix.

3. Targeted hints for the two most-hallucinated APIs

list.zip → list.enumerate, or compare via str.join(a, ",") == str.join(b, ",").
str.to_str → int.to_str from std.int.

Both verified absent on 0.10.6 before the hint was written — the linter should never assert an API doesn't exist without that being checked.

Verification

CI's own loop, run locally on 0.10.6:

for f in $(git ls-files src/ | grep '\.lex$'); do lex check "$f"; done
  exit=0   (76 files)
lex check examples/manifesto_parallel.lex
  ok

Note

The fix to the index matters more than the lint rule: the rule catches the symptom, the index was the cause. The rule stays as a safety net for models that reach for zip out of habit from other languages.

🤖 Generated with Claude Code