export default function(node, {evaluate, scope}) {
  const {argument, operator, prefix} = node;
  const {value} = evaluate(argument, {scope});
  const update = (value) => {
    if (prefix) {
      switch (operator) {
        case '++': return scope.set(argument.value, value + 1);
        case '--': return scope.set(argument.value, value - 1);
      }
    }
    switch (operator) {
      case '++':
        scope.set(argument.value, value + 1);
        return value;
      case '--':
        scope.set(argument.value, value - 1);
        return value;
    }
    /* v8 ignore next */
    throw new Error(`operator not implemented: ${operator}`);
  };
  return {value: update(value)};
}