iostream.pl -- Utilities to deal with streams
This library contains utilities that deal with streams, notably originating from non-built-in sources such as URLs, archives, windows, processes, etc.
The predicate open_any/5 acts as a broker between applications that
can process data from a stream and libraries that can create streams
from diverse sources. Without this predicate, processing data inevitally
follows the pattern below. As call_some_open_variation can be
anything, this blocks us from writing predicates such as
DOM) that can operate on arbitrary input sources.
setup_call_cleanup( call_some_open_variation(Spec, In), process(In), close(In)).
Libraries that can open streams can install the hook iostream:open_hook/6 to make their functionality available through open_any/5.
- open_any(+Specification, +Mode, -Stream, -Close, +Options)
- Establish a stream from Specification that should be closed
using Close, which can either be called or passed to
close_any/1. Options processed:
- Set stream to encoding Enc.
Without loaded plugins, the open_any/5 processes the following values for Specification. If no rule matches, open_any/5 processes Specification as
- A plain stream handle. Possisible post-processing options such as encoding are applied. Close does not close the stream, but resets other side-effects such as the encoding.
- Same as a plain Stream.
- If Specification is of the form =file://...=, the pointed to file is opened using open/4. Requires library(uri) to be installed.
- Explicitly open the file Path. Path can be an Path(File) term as accepted by absolute_file_name/3.
- Open a Prolog string, atom, list of characters or codes as an input stream.
The typical usage scenario is given in the code below, where <process> processes the input.
setup_call_cleanup( open_any(Spec, read, In, Close, Options), <process>(In), Close).
Currently, the following libraries extend this predicate:
- Adds support for URLs using the
- Execute the Close closure returned by open_any/5. The closure can also be called directly. Using close_any/1 can be considered better style and enhances tractability of the source code.