\libdoc{registry}{Manipulating the Windows registry}

The \pllib{registry} is only available on the MS-Windows version of
SWI-Prolog. It loads the foreign extension \file{plregtry.dll},
providing the predicates described below. This library only makes the
most common operations on the registry available through the Prolog
user. The underlying DLL provides a more complete coverage of the
Windows registry API. Please consult the sources in
\file{pl/src/win32/foreign/plregtry.c} for further details.


In all these predicates, \arg{Path} refers to a `/' separated path
into the registry.  This is \emph{not} an atom containing `/'-characters
as used for filenames, but a term using the functor \functor{/}{2}.
Windows defines the following roots for the registry:
\const{classes_root},
\const{current_user},
\const{local_machine} and
\const{users}.


\begin{description}
    \predicate{registry_get_key}{2}{+Path, -Value}
Get the principal (default) value associated to this key. Fails silently
if the key does not exist.

    \predicate{registry_get_key}{3}{+Path, +Name, -Value}
Get a named value associated to this key.

    \predicate{registry_set_key}{2}{+Path, +Value}
Set the principal (default) value of this key.  Creates (a path to) the key
if it does not already exist.

    \predicate{registry_set_key}{3}{+Path, +Name, +Value}
Associate a named value to this key. Creates (a path to) the key
if it does not already exist.

    \predicate{registry_delete_key}{1}{+Path}
Delete the indicated key.

    \predicate{shell_register_file_type}{4}{+Ext, +Type, +Name, +OpenAction}
Register a file-type. \arg{Ext} is the extension to associate.
\arg{Type} is the type name, often something like \const{prolog.type}.
\arg{Name} is the name visible in the Windows file-type browser.
Finally, \arg{OpenAction} defines the action to execute when a file with
this extension is opened in the Windows explorer.

    \predicate{shell_register_dde}{6}{+Type, +Action, +Service, +Topic,
				      +Command, +IfNotRunning}
Associate DDE actions to a type. \arg{Type} is the same type as used for
the 2nd argument of shell_register_file_type/4, \arg{Action} is the
action to perform, \arg{Service} and \arg{Topic} specify the DDE topic
to address, and \arg{Command} is the command to execute on this topic.
Finally, \arg{IfNotRunning} defines the command to execute if the
required DDE server is not present.

    \predicate{shell_register_prolog}{1}{+Ext}
Default registration of SWI-Prolog, which is invoked as part of the
initialisation process on Windows systems.  As the source also includes
the above predicates, it is given as an example:

\begin{code}
shell_register_prolog(Ext) :-
	current_prolog_flag(argv, [Me|_]),
	atomic_list_concat(['"', Me, '" "%1"'], OpenCommand),
	shell_register_file_type(
	    Ext, 'prolog.type', 'Prolog Source', OpenCommand),
	shell_register_dde(
	    'prolog.type', consult,
	    prolog, control, 'consult(''%1'')', Me),
	shell_register_dde(
	    'prolog.type', edit,
	    prolog, control, 'edit(''%1'')', Me).
\end{code}
\end{description}