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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 125 |
1 files changed, 125 insertions, 0 deletions
@@ -26554,6 +26554,131 @@ may be applied to the third argument of the .code *unhandled-hook* function to obtain more information about the form. +.coNP Macro @ defex +.synb +.mets (defex <> { symbol }*) +.syne +.desc +The macro +.code defex +records hierarchical relationships among symbols, for the purposes +of the use of those symbols as exceptions. It is closely related to the +.code @(defex) +directive in the \*(TX pattern language, performing the same function. + +All symbols are considered to be exception subtypes, and every symbol +is implicitly its own exception subtype. This macro does not introduce +symbols as exception types; it only introduces subtype-supertype +relationships. + +If +.code defex +is invoked with no arguments, it has no effect. + +If arguments are present, they must be symbols. + +If +.code defex +is invoked with only one symbol as its argument, it has no effect. + +At least two +symbols must be specified for a useful effect to take place. If exactly two +symbols are specified, then, subject to error checks, +.code defex +makes the left symbol an +.I exception subtype +of the right symbol. + +This behavior generalizes to three or more arguments: if three or more symbols +are specified, then each symbol other than the last is registered as a subtype of +the symbol which follows. + +If a +.code defex +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 +to attempt to specify it as a supertype in a registration. +Using +.code nil +as a subtype in a registration is silently permitted, but has no effect. +No explicit registration is recorded between +.code nil +and its successor in the argument list. + +The symbol +.code t +is implicitly the supertype of every exception type. Therefore, it +is erroneous to attempt to register it as an exception subtype. +Using +.code t +as a supertype in a registration is also erroneous. + +Keyword symbols may be used as exception types. + +.coNP Function @ register-exception-subtypes +.synb +.mets (register-exception-subtypes <> { symbol }*) +.syne +.desc +The +.code register-exception-subtypes +function constitutes the underlying implementation for the +.code defex +macro. + +The following equivalence applies: + +.cblk + (defex a b ...) <--> (register-exception-subtypes 'a 'b ...) +.cble + +That is, the +.code defex +macro works as if by generating a call to the function, with +the arguments quoted. + +The semantics of the function is precisely that of the macro. + +.coNP Function @ exception-subtype-p +.synb +.mets (exception-subtype-p < left-symbol << right-symbol ) +.syne +.desc +The +.code exception-subtype-p +function tests whether two symbols are in a relationship as exception types, +such that +.meta left-symbol +is a direct or indirect exception subtype of +.metn right-symbol . + +If that is the case, then +.code t +is returned, otherwise +.codn nil . + .SS* Regular Expression Library .coNP Functions @ search-regex and @ range-regex .synb |