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|Pack with -- prolog/with.pl|
This module provides context management for various types of Prolog
objects, such as IO streams, dynamic clauses, and settings. User
defined contexts can be implemented using the multifile predicate
manage_context(Term, Setup, Cleanup) defines a
setup/cleanup pair for a specific type of term.
Goal using setup_call_cleanup/3, with the corresponding setup
and cleanup goals.
There is one difference between the semantics of setup_call_cleanup/3
and the corresponding goal using this library.
goals must succeed. If they fail, the error
`error(mode_error(must_succeed, FailingGoal))` is thrown.
For example, the provided manage_context/3 clause for opening files could be defined:
with:manage_context(open(File, Mode, Stream), open(File, Mode, Stream), close(Stream)).
The result is that the following are equivalent:
?- setup_call_cleanup(open(File, read, Stream), is_stream(Stream), close(Stream)). ?- use_module(library(with)), with(open(File, read, Stream), is_stream(Stream)).
To show defined context managers, using
`listing/1`. E.g, the
context managers packaged with this module are:
?- use_module(library(with)), listing(with:manage_context/3). manage_context(open(A, C, D), (absolute_file_name(A, B), open(B, C, D)), close(D)). manage_context(assertz(A), assertz(A, B), erase(B)). manage_context(setting(A, B), (setting(A, C), set_setting(A, B)), set_setting(A, C)).