generate_message_hook/3 hook:- multifile user:generate_message_hook/3.
user:generate_message_hook(+MessageTerm, -S0, -S)
A way for the user to override the call to 'SU_messages':generate_message/3
in print_message/2.
term
May be any term.
list of pair
The resulting list of Control-Args pairs.
list of pair
The remaining list.
For a given MessageTerm, generates the list of
Control-Args pairs required for print_message_lines/3 to
format the message for display.
This is the same as 'SU_messages':generate_message/3 except
that it is a hook. It is intended to be used when you want to
override particular messages from the Prolog system, or when you want
to add some messages. If you are using your own exception classes
(see raise_exception/1) it may be useful to provide
generate_message_hook clauses for those exceptions so that the
print_message/2 (and thus the default exception handler that
calls print_message/2) can print them out nicely.
The Prolog system uses the built-in predicate print_message/2
to print all its messages. When print_message/2 is called, it
calls user:generate_message_hook(Message,L,[]) to generate the
message. If that fails,
'SU_messages':generate_message(Message,L,[]) is called instead.
If that succeeds, L is assumed to have been bound to a list whose
elements are either Control-Args pairs or the atom nl. Each Control-Arg
pair should be such that the call
format(user_error, Control, Args)
is valid. The atom nl is used for breaking the message into
lines. Using the format specification ‘~n’ (new-line) is
discouraged, since the routine that actually prints the message (see
user:message_hook/3 and print_message_lines/3) may need
to have control over newlines.
:- multifile user:generate_message_hook/3.
user:generate_message_hook(hello_world) -->
['hello world'-[],nl].
Note that the terminating nl is required.
All error handling is done by the predicates extended by this hook.