The predicate input-stream-p
is implemented as a generic function. The default method returns t
if stream is an input stream. If the user wants to implement a stream with no inherent directionality (and thus does not include fundamental-input-stream or fundamental-output-stream) but for which the directionality depends on the instance, then a method should be provided for input-stream-p
.
There is an example in Stream directionality.
LispWorks User Guide and Reference Manual - 13 Feb 2015