[r6rs-discuss] Mixed binary and ascii data in a single file

From: Bradley Lucier <lucier>
Date: Wed, 8 Aug 2007 13:44:05 -0400

The old pbm/pgm/ppm/pnm file format follows a few lines of ASCII
header information at the top of a file with the bytes/octets of the
image data. So you have to switch from ASCII to binary at a very
particular point in the file.

In gambit you have "read", which does the usual thing, and read-u8,
which appears to do a similar thing as get-u8 in (rnrs io ports (6)).

So I have two questions.

If you turn off buffering in gambit, you can switch between using
"read" and using "read-u8" without problems.

Is there any way to do that in (rnrs io ports (6))? It appears on my
first reading that the answer is no.

In gambit, after I stop reading the header information (which must
use unbuffered reads, because I don't want any lookahead), I can
change the port buffering to #t (allowing buffering again), which
speeds up the reading of the rest of the file, even an octet at a
time in in a loop that makes several function calls for each byte, by
more than an order of magnitude.

So my second question is: Is there any way to change the buffering of
a port after it's been opened in (rnrs io ports (6))?

And a meta-question is: Leaving aside how these things are done in
Gambit, how can I achieve what I want to do (mixed ASCII and binary
data, buffered reads of the binary data) in (rnrs io ports (6))?

Brad
Received on Wed Aug 08 2007 - 13:44:05 UTC