Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Fix a spreadsheet formula engine (precedence, error values, static cycle detection, 5,000-cell chains without recursion errors)

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  "result": "I rewrote `sheet.py` to implement `SHEET_RULES.md`. It uses only the standard library and never passes cell text to `eval`/`exec`. `evaluate(grid)` keeps its name and signature, and the CLI (`python3 sheet.py in.csv out.csv`) works.\n\n**How it works:** each formula is tokenized and compiled to postfix code by a recursive-descent parser, then run on a stack. Cycles are found with an iterative Tarjan pass over the static reference graph, which includes both `IF` branches and every cell in a range. Components are evaluated dependencies-first, so no recursion is needed across cells.\n\n**Verification:** my 22-test suite is in `/tmp/sheet_tests/test_sheet.py`, outside the repo. It covers each numbered rule, the CLI round-trip, the 5,000-cell chain, and robustness cases. A randomized check of cycle detection against a naive reachability computation (1,500 random grids) found no mismatches. The hidden grader may still differ on cases the spec leaves open; I can't check those.\n\n**Timings:** a 10,000-cell chain takes 0.13s. A 100\u00d7100 grid where 1,000 cells each sum a 100\u00d710 block takes 0.13s. A 10,000-formula running-total column (`=SUM(B$1:Bn)`, O(n\u00b2) reads) takes about 26s, which misses the \"under 5 seconds\" line for that shape. Fixing it would need a different range data structure, which I didn't build. Say if you want that.\n\n**Choices where the spec was silent:**\n- A parenthesised single reference such as `SUM((A1))` counts as a single reference, so empty and text cells are ignored.\n- Unary `+` converts its operand to a number.\n- Errors inside a range propagate even for `COUNT`.\n- An unknown function returns `#NAME?` without propagating its arguments' errors.\n- A negative base with a fractional exponent (`(-8)^(1/3)`) gives `#VALUE!`.\n- Power overflow gives \u00b1inf.\n- A syntax-error formula that sits on a cycle shows `#CYCLE!`, because rule 8 says every formula on a cycle does.\n- A row number too large to fit the grid is treated as an empty cell.\n\nThis directory is not a git repo, so I did not commit anything.",
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