isOpen returns true if the input source is open for reading, false otherwise.
"Open" in this context is whether the InputSource object is currently open,
meaning that it is the front element of the InputSourceRange that created it.
For files, this is also reflected in the state of the underlying File object.
However, standard input is never actually closed.
isOpen returns true if the input source is open for reading, false otherwise.
"Open" in this context is whether the InputSource object is currently open, meaning that it is the front element of the InputSourceRange that created it.
For files, this is also reflected in the state of the underlying File object. However, standard input is never actually closed.