Lisp Expression Parser

Parse expression as one Lisp-style expression and return the canonical JSON serialization of its syntax tree as a string.

• An atom is a nonempty maximal sequence of ASCII letters, digits, underscore, plus, minus, asterisk or slash. Preserve its exact characters and case, including leading zeros and signs.
• A list consists of an opening parenthesis, zero or more expressions, and a closing parenthesis. Lists may nest.
• ASCII space, tab, line feed and carriage return separate tokens and may occur before or after the root. Parentheses are standalone tokens even when adjacent to atoms or other parentheses.
• The input is valid and contains exactly one root expression. Adjacent atoms must be separated by whitespace; parentheses already provide token boundaries.

Serialize every atom as a JSON string and every list as a JSON array of its children, preserving their order and nesting. Use commas between children and no whitespace outside quoted atom strings. The allowed atom characters never contain a quote or backslash. An empty list becomes [].