Function identifier

src/math-json/parse-sympy.ts:38–45

(
  s: string,
  i: number
)

}

function identifier(
  s: string,
  i: number
): [i: number, result: Expression | null] {
  const m = s.slice(i).match(/^[\p{XIDS}_][\p{XIDC}]*/u);
  if (m === null) return [i, null];
  return [i + m[0].length, symbol(m[0])];
}

function exponent(s: string, i: number): [i: number, result: string | null] {
  if (s[i] !== 'e' && s[i] !== 'E') return [i, null];