[MLton-devel] Re: SML Basis review

[Matthew Fluet]

BTW, the context of this is Chapter 8 of the SML Basis.  Under a section
titled "Comparision of I/O functions" there is a statement:

 * Stream I/O input is more efficient than Imperative I/O input.  At the
   least, the latter will require an extra indirection and assigment per
   operation.

I commented:

This is not necessarily true.  Both PolyML and MLton provide a "direct"
imperative buffered I/O layer so long as the underlying stream is not
extracted.  This can be significantly more efficient than the
ref StreamIO.instream  version.

On Mon, 18 Aug 2003, Matthew Fluet wrote:

> > Concerning the comparison of Imperative vs. Stream I/O input in MLton and
> > PolyML, are you saying that
> >
> >   Imperative I/O is faster than Stream I/O
> >
> > or that
> >
> >   Imperative I/O is no slower than Stream I/O
> >
> > assuming, of course, the underlying stream is not extracted?
>
> The former: Imperative I/O is faster than Stream I/O, assuming that the
> underlying stream is not extracted.
>
> Note that which input function one uses impacts how great the difference.
> The extreme example is input1: Under Stream IO, each input generates a
> large data structure (relative to the 1 byte that was returned)
> corresponding to the stream advanced by one byte.  This results in more
> allocation time, more GCs, etc.  Under the Buffered I (i.e., the special
> case of the Imperative IO), we simply update an integer ref corresponding
> to the current position in an array of buffered input.
>
> I have a slew of benchmarks that perform a line count on a file using each
> of the ImperativeIO and StreamIO input functions, comparing with and
> without forcing the underlying stream, and using various implementations.
> I could run them again if anyone wants hard numbers.
>
>
>
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