[m-dev.] comments on binary input streams and bytes as ints

[Julien Fischer]

Hi Zoltan,

Commit 5951724 adds the following XXX comments.
Here are my comments about those comments.

+:- instance stream.reader(binary_input_stream,         int,   io,
io.error).
+:- instance stream.reader(binary_input_stream,         int8,  io,
io.error).
+:- instance stream.reader(binary_input_stream,         uint8, io,
io.error).
+% XXX IO_INSTANCE reader for int calls read_byte

The use of int here is a legacy usage in the standard library.
Historically, it has represented a "byte" using the lower 8 bits on int.

Now that we have proper 8 bit sized types, the "byte is the lower 8 bits
of an int" approach should be deprecated.  (I think I have already added
uint8/int8 alternatives for all the affected operations.)

+% XXX IO_INSTANCE inconsistent: no instance for uint

No such instance should be added.

+:- instance stream.unboxed_reader(binary_input_stream, int8,  io,
io.error).
+:- instance stream.unboxed_reader(binary_input_stream, uint8, io,
io.error).
+% XXX IO_INSTANCE no instance for int

unboxed_readers were added *after* fixed size integers; I didn't think
there is any point adding an int version only to eventually remove it.

+:- instance stream.putback(binary_input_stream,        int,   io,
io.error).
+:- instance stream.putback(binary_input_stream,        int8,  io,
io.error).
+:- instance stream.putback(binary_input_stream,        uint8, io,
io.error).
+% XXX IO_INSTANCE putback for int calls putback_byte
+% XXX IO_INSTANCE inconsistent: no instance for uint

As above.

Julien.