[R6RS] Protocol for handling encoding/decoding errors
sperber at informatik.uni-tuebingen.de
Thu Aug 24 10:58:32 EDT 2006
Here's a first cut at it, mainly for Will:
For encoding errors, i.e. putting text on an output port:
The idea is that, when the error is raised, the output port points
past the character that caused the error. A continuable exception
with condition type &i/o-encoding is raised, with the following
(define-condition-type &i/o-encoding &i/o-port
The exception handler must `put-bytes' or whatever onto the port. Its
return values would be ignored.
Continuing means picking up after that character. I.e., `put-string'
will continue after the character that caused the error.
For decoding errors, i.e. getting text from an input port:
When the error is raised, the input port points at the beginning of
the incorrect encoding. A continuable exception with condition type
&i/o-decoding is raised, with the following definition:
(define-condition-type &i/o-decoding &i/o-port
The exception handler must return a character or string representing
the decoded text starting at the port's current position, and update
the port's position to point past the error.
This has the disadvantage that a handler may want to try handling the
error, decline and leave the handling to some higher-level handler,
but that "try handling" involves removing data from the port, which is
not reversible. I don't know an easy way around this.
Continuing means continuing the operation as though the returned
string had been read from the input. Consider `get-line' seeing this:
with an exception handler like so:
(get-byte (i/o-error-port c))
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla
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