Status: Version 3 passed, 6/8/90
References: Condition System, Version 18
Edit History: Version 1, 1/3/90 by Kim A. Barrett
Version 2, 6/6/90 by Kim A. Barrett
Version 3, 6/11/90 by Kim A. Barrett (X3J13 ammendments)
The recently passed issue READER-ERROR defined the new condition type
PARSE-ERROR as a subtype of STREAM-ERROR. This means that PARSE-ERROR
inherits behavior on the function STREAM-ERROR-STREAM, and has :STREAM as
the associated initarg. The description of STREAM-ERROR can be read to
imply that the value of STREAM-ERROR-STREAM is in fact a STREAM. That is,
that (TYPEP (STREAM-ERROR-STREAM c) 'STREAM) -> true. However, it is fairly
easy to imagine a program which might want to signal PARSE-ERROR under some
circumstance, but which is not using a Common Lisp stream as its source of
1. Define that PARSE-ERROR has the class precedence list
(PARSE-ERROR ERROR SERIOUS-CONDITION CONDITION T)
thus making it no longer be a subtype of STREAM-ERROR.
2. Define a new condition called READER-ERROR, with class precedence list
(READER-ERROR PARSE-ERROR STREAM-ERROR ERROR SERIOUS-CONDITION CONDITION T).
Issue READER-ERROR (version 3, passed 11/89) specified that the reader was to
signal errors of type PARSE-ERROR for serious conditions that relate to
lexical analysis (the building and interpretation of tokens) and parsing
(errors in reader macro syntax) by the Lisp reader. Change this to instead
specify that the reader signals errors of type READER-ERROR for such
situations. There are numerous places (especially in chapter 3) that would
SPLIT-TYPES fixes the problem in the obvious way. If a program needs a
condition which inherits from both is desired, such a condition can be
trivially defined, since issue CLOS-CONDITIONS says that we now have
multiple inheritance for conditions.
PARSE-ERROR is sufficiently new that few implementations are likely to
have added it.
Cost to Implementors:
Should be trivial.
Cost to Users:
If this does not passe then some programs which might otherwise reasonably
signal PARSE-ERRORs will not be able to do so.
Barrett supports SPLIT-TYPES. He had some qualms about the merging when
he first saw the READER-ERROR issue, but didn't have time to think about
it much before the issue was voted on.