function numberEvaluator(flatStyle, name, context) {
  if (!(name in flatStyle)) {
    return undefined;
  }
  const evaluator = buildExpression(flatStyle[name], NumberType, context);
  return function (context) {
    return requireNumber(evaluator(context), name);
  };
}
@param {FlatStyle} flatStyle The flat style.
@param {string} name The property name.
@param {ParsingContext} context The parsing context.
@return {import('../../expr/cpu.js').NumberEvaluator|undefined} The expression evaluator or undefined.