[r6rs-discuss] Behaviour of lookahead-u8 and lookahead-char on custom ports
xacc.ide at gmail.com
Thu Aug 7 12:16:59 EDT 2008
From: "William D Clinger"
> Similarly, custom input/output ports cannot work
> reliably in general, because there is no way for
> the i/o system to tell a custom port to correct for
> a lookahead byte or character when switching from
> input to output.
I just came to that conclusion earlier today.
> Thirdly, and more broadly, all textual input/output
> ports whose transcoders use variable-width encodings
> (or use end-of-line styles other than none) have
> problematic and/or partially undefined semantics.
> Output operations that overwrite a character (or
> end-of-line) with a character whose encoding is of
> a different length have undefined semantics.
Havent event gotten there yet!
> All three of these bugs have been documented for some
> time in Larceny's list of deprecated R6RS syntax and
> procedures .
Pity Google turned up nothing on it.
Thanks for the input.
I guess it's a matter of 'do the best you can of the situation' and raise
exceptions when used in an unhandled/unsupported manner.
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