Claude Sonnet 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": "I wrote the interpreter in `tiny.py` (`run` and `TinyError`, standard library only). I ran a handful of programs by hand. I did not write a test suite or run anything beyond those.\n\nWhat those checks showed:\n- **Error messages and line numbers:** these matched the spec for redeclaration, a chained comparison, an undefined variable, division by zero and `return` outside a function.\n- **Call-depth limit:** a recursive function nested 200 calls deep ran, and the call that would be the 201st failed with `stack overflow` at that call's line. It runs the interpreter in a thread with a large stack, so Python itself doesn't crash.\n- **Arithmetic and printing:** `-7 % 3` and `-7 / 2` came out as the spec says, and `print` of a function and of a string repeat worked.\n\nThe spec doesn't settle a few things, so I picked:\n- **Function body scope:** a function's body shares the scope that holds its parameters, so `let` of a parameter name inside the body is an `already declared` error.\n- **`let` evaluation order:** the right-hand side of a `let` is evaluated before the redeclaration check.\n- **Call error line:** for a call, errors are reported at the line of the opening `(`.\n- **`else` on its own line:** `else` must follow the `}` on the same line, so an `else` that starts its own line is a syntax error.\n- **Leniency:** block statements (`if`, `while`, `fn`) don't need a terminator after their closing `}`. A second statement on the same line right after a `}` is accepted rather than rejected.",
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