Function toBigint

src/compute-engine/boxed-expression/numerics.ts:201–222

(expr: Expression | undefined)

 * integer parameters a collection handler reads (a `Take` count, a
 * `RotateLeft` offset, an `InsertAt` position).
 *
 * Collection handlers are consulted on the *canonical* expression, not on an
 * evaluated one: `.at()`/`.each()`/`.count` are public on any canonical
 * expression, and the pre-evaluation broadcast in
 * `BoxedFunction._computeValue` zips raw operands. A parameter spelled `N-1`
 * is therefore still an `Add` node at that point, where a bare `toInteger`
 * answers `null` — which every call site turned into its own DEFAULT
 * (`?? 1`, `?? 0`), silently substituting a different collection:
 * `RotateLeft(S, N-1) + RotateLeft(S, N-2)` answered `2·RotateLeft(S, 1)`
 * (Tycho item 107).
 *
 * `toInteger` runs first, so a literal operand — the hot path of a drain —
 * costs nothing extra; only a symbolic operand pays one `evaluate()`. An
 * operand that is already a number literal is never re-evaluated: if it is
 * not an integer, no amount of evaluation will make it one.
 */
export function toIntegerOperand(expr: Expression | undefined): number | null {
  const n = toInteger(expr);
  if (n !== null) return n;
  if (expr === undefined || isNumber(expr)) return null;
  return toInteger(expr.evaluate());
}

/** Convert a boxed expression to a bigint.
 * Returns null if the expression cannot be converted to a bigint.