[Sml-implementers] Basis library

[David M. <Dav...@de...>]

I've been having another look at the Basis library implementation in=20
Poly/ML and in particular the I/O library.  I'm still not sure I fully=20=

understand the implications of the Stream IO (functional IO) layer and=20=

in particular the way "canInput" works and interacts with "input".

The definition says that canInput(f, n) returns SOME k "if a call to=20
input would return immediately with at least k characters". =20
Specifically it does not say "if a call to inputN(f, k) would return=20
immediately".   Secondly it says that it "should attempt to return as=20
large a k as possible" and gives the example of a buffer containing 10=20=

characters with the user calling canInput(f, 15).  This suggests that a=20=

call to canInput could have the effect of committing the stream since a=20=

perfectly good implementation of "input" would be to return what was=20
left of the buffer, i.e. 10 characters, and only read  from the=20
underlying stream on a subsequent call to "input".  Yet after a call to=20=

canInput(f, 15) which returns SOME 15 the call to "input" is forced to=20=

return at least 15.  In other words a call to canInput changes the=20
behaviour of a subsequent call to "input".  Generally, what is the=20
behaviour of canInput with an argument larger than the buffer size?  How=20=

far ahead is canInput expected to read?

A few other notes of things I've discovered, some of which are trivial:

The signature for TextIO.StreamIO contains duplicates of
=A0=A0where=A0type=A0StreamIO.reader=A0=3D=A0TextPrimIO.reader
=A0=A0where=A0type=A0StreamIO.writer=A0=3D=A0TextPrimIO.writer

There are declared constants for platformWin32Windows2000 and=20
platformWin32WindowsXP in the Windows structure.  When I proposed the=20
Windows.Config structure I didn't include constants for these versions=20=

of the OS because the underlying GetVersionEx function returns the same=20=

value, VER_PLATFORM_WIN32_NT in the dwPlatformId field for NT, Windows=20=

2000 and XP   It is possible to distinguish these but only using the=20
major and minor version fields.  Windows CE does give a different value=20=

for the platformID.  I would say it is confusing to have these here=20
because it implies that it's possible to discriminate on the basis of=20
the platformID field.

The example definition of input1 at the bottom of STREAM_IO returns a=20
value of type elem option * instream when the signature says it should=20=

be (elem * instream) option.

Description of "input" function in STREAM_IO signature.  The word "ay"=20=

should be "may".

--
David.