FA-217 / Parsing / Member archive

A separator inside nested brackets splits the outer list · case 02

A comma inside a nested expression becomes a top-level boundary, or mismatched brackets pass unchecked.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Split a comma-separated expression into trimmed top-level fields using (), [], and {} nesting. Preserve empty fields, return [] for an empty string, and return None for mismatched or unclosed brackets. Quotes and escapes have no special meaning in this restricted grammar.

Why this case matters

Command and configuration mini-languages often embed collections inside argument lists. Typed nesting is needed even before adding full expression parsing.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
nested parentheses	`["((a", "b))", "tail"]`	`["((a,b))", "tail"]`	Failed

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