Computation hGetContents hdl returns the list of characters
corresponding to the unread portion of the channel or file managed
by hdl, which is put into an intermediate state, semi-closed.
In this state, hdl is effectively closed,
but items are read from hdl on demand and accumulated in a special
list returned by hGetContents hdl.
Any operation that fails because a handle is closed,
also fails if a handle is semi-closed. The only exception is hClose.
A semi-closed handle becomes closed:
- if hClose is applied to it;
- if an I/O error occurs when reading an item from the handle;
- or once the entire contents of the handle has been read.
Once a semi-closed handle becomes closed, the contents of the
associated list becomes fixed. The contents of this final list is
only partially specified: it will contain at least all the items of
the stream that were evaluated prior to the handle becoming closed.
Any I/O errors encountered while a handle is semi-closed are simply
discarded.
This operation may fail with:
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