Claude Haiku 5.5 (effort default (no --effort flag) · thinking on) on Write a lexer, parser and evaluator for a small closure-based language from a 1-page spec

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  "result": "`tiny.py` now implements `run(source)` and `TinyError` per `SPEC.md`, using only the standard library. I checked it with a scratch test script outside the work directory. It covers arithmetic, scoping, closures, recursion, and the error messages and line numbers. The only three failures were wrong expectations in my script, and the interpreter's behaviour is correct for them.\n\n- **Call depth:** exactly 200 nested calls succeed. The 201st fails with `line N: stack overflow` at its own call line. Infinite recursion gives the same error without crashing Python.\n- **Deep nesting:** 5000-deep parenthesised expressions parse and run, and pathological nesting that exhausts the recursion limit is reported as a Tiny syntax or stack error rather than a Python traceback.\n\nThe spec left some cases open, so I chose these:\n\n- **Newlines in brackets:** a newline is ignored only when the innermost open bracket is `(`. Inside a `{ }` body nested in a call, newlines still end statements.\n- **Function scope:** parameters and the function body share one scope, so `fn f(a) { let a = 1 }` gives `already declared`.\n- **Duplicate parameters:** `fn f(a, a)` is reported as `already declared` when the function is called, not when it is defined.\n- **`return outside function`:** raised when the statement executes, not at parse time.\n- **Check order:** on a call, the type check runs first, then arity, then stack depth.\n- **`let` and assignment:** the right-hand side is evaluated before the already-declared or undefined-variable check.\n- **Lexer errors:** unknown escapes, unterminated strings, and stray characters like `!` are `line N: syntax error`.\n- **Global side effects:** `run` temporarily raises the Python recursion limit to 50000 and restores it afterwards. Importing the module also lifts Python's 4300-digit limit on int\u2194str conversion, which is process-wide, so that every Tiny integer prints in full.\n\nNothing is committed; the directory is not a git repository.",
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