The function name should be "beep_nodeapi" rather than "hook_nodeapi". The hook itself is named hook_nodeapi(). The hooked version for the module needs to be name [module name]_nodeapi().

I've left the path of strict and verbatim obedience to the book's prescription, and defined the actions in a module that had already been installed. The actions didn't show up in the user interface. In Drupal 6.6, which is what I'm using, you have to click on admin/settings/actions in order for the actions to be registered in the actions table, whence they are retrieved to be displayed in the dropdown menus on admin/build/trigger.

Minor suggestion: a reminder to enable the Beep module would be helpful.

In my paper copy and the electronic version that I just downloaded (30 Jan 09) from the APress Website, the code in wrong near the top of page 47. Off by one error. Loop will terminate early. The problem does not exist in the downloadable code.

array_merge() appends values instead of combining them when keys are numeric, as they are implicitly in the above array.

drupal_alter is a generic dispatching mechanism used for many hooks. That it is used to dispatch hook_action_info_alter is an irrelevant and confusing implementation detail. (Note: the same error should be corrected in the comment for the code example beneath the heading.)

Point is made clear -- just a small oversight on what the callback function of the configurable function 'beep_multiple_beep_action' is as opposed to the chapters non-configurable counterpart, 'beep_beep_action'.

The code relies on the inheritance of menu access callbacks. During the writing of the book, Drupal changed to no longer do inheritance so access arguments must be declared explicitly (see "Note for Module Developers" here). The code example slipped through final technical review of the book.