Function boxRule

src/compute-engine/boxed-expression/rules.ts:723–877

(
  ce: ComputeEngine,
  rule: Rule | BoxedRule,
  options?: { canonical?: boolean; purpose?: RulePurpose }
)

    }

    return boxRule(
      ce,
      { match, replace, condition: condFn, id: rule },
      options
    );
  } finally {
    // Pop the clean scope AFTER canonicalization to avoid pollution
    if (systemScope) {
      ce.popScope();
    }
  }
}

function boxRule(
  ce: ComputeEngine,
  rule: Rule | BoxedRule,
  options?: { canonical?: boolean; purpose?: RulePurpose }
): BoxedRule {
  if (rule === undefined || rule === null)
    throw new Error('Expected a rule, not ' + rule);

  if (isBoxedRule(rule)) {
    // Apply the default purpose to already-boxed rules that don't carry
    // their own tag (a per-rule tag takes precedence).
    if (options?.purpose !== undefined && rule.purpose === undefined)
      return { ...rule, purpose: options.purpose };
    return rule;
  }

  // If the rule is defined as a single string, parse it
  // e.g. `|x| -> x; x > 0`
  if (typeof rule === 'string') return parseRule(ce, rule, options);

  // If the rule is defined as a function, the function will be called
  // on every expression to process it.
  if (typeof rule === 'function')
    return {
      _tag: 'boxed-rule',
      match: undefined,
      replace: rule,
      condition: undefined,
      purpose: options?.purpose,
      id: rule.toString().replace(/\n/g, ' '),
    };

  // eslint-disable-next-line prefer-const
  let { match, replace, condition, id, onMatch, onBeforeMatch, operators } =
    rule;

  // The per-rule purpose tag takes precedence over the per-ruleset default
  const purpose = rule.purpose ?? options?.purpose;

  if (replace === undefined)
    throw new Error(
      `Invalid rule "${
        id ?? JSON.stringify(rule, undefined, 4)
      }"\n|   A rule must include at least a replace property`
    );