diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 22 |
1 files changed, 9 insertions, 13 deletions
@@ -41752,23 +41752,10 @@ has three or more arguments, they are processed from left to right. If errors are encountered during the processing, the correct registrations already made for prior arguments remain in place. -It is erroneous to register a duplicate relationship. If symbol -.code a -is already a direct or indirect subtype of -.code b -then -.code "(defex a b)" -and -.code "(defex a x b)" -are erroneous. - Every symbol is implicitly considered to be its own exception subtype, therefore it is erroneous to explicitly register a symbol as its own subtype. -The foregoing rules eliminate the possibility of creating cycles in the -exception subtype inheritance graph. - The symbol .code nil is implicitly a subtype of every exception type. Therefore, it is erroneous @@ -41788,6 +41775,15 @@ Using .code t as a supertype in a registration is also erroneous. +A symbol +.code a +may not be registered as a subtype of a symbol +.code b +if the reverse relationship already exists between those two symbols. + +The foregoing rules allow redefinitions to take place, while forbidding cycles +from being created in the exception subtype inheritance graph. + Keyword symbols may be used as exception types. .coNP Function @ register-exception-subtypes |