Specifies the application context that identifies the application.
Specifies the argument that is to be passed to the specified procedure
when input is available.
Specifies the mask that indicates a read, write, or exception condition
or some operating system dependent condition.
Specifies the ID returned from the corresponding
Specifies the procedure that is to be called when input is available.
Specifies the source file descriptor on a UNIX-based system
or other operating system dependent device specification.
function registers with the Intrinsics read routine a new source of events,
which is usually file input but can also be file output.
Note that file should be loosely interpreted to mean any sink
or source of data.
also specifies the conditions under which the source can generate events.
When input is pending on this source,
the callback procedure is called.
The legal values for the condition argument are operating-system dependent.
On a UNIX-based system,
the condition is some union of
function causes the Intrinsics read routine to stop watching for input
from the input source.