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PL_raise_exception() |
FALSE
. If there is already a pending exception,
the most urgent exception is kept; and if both are of the same urgency,
the new exception is kept. Urgency of exceptions is defined as
'$aborted'
).time_limit_exceeded
(see call_with_time_limit/2).resource_error
exceptions.error(Formal, ImplDef)
exceptions.
This function is rarely used directly. Instead, errors are typically
raised using the functions in section
12.4.7 or the C api functions that end in _ex
such as PL_get_atom_ex().
Below we give an example returning an exception from a foreign predicate
the verbose way. Note that the exception is raised in a sequence of
actions connected using &&
. This ensures that a
proper exception is raised should any of the calls used to build or
raise the exception themselves raise an exception. In this simple case PL_new_term_ref()
is guaranteed to succeed because the system guarantees at least 10
available term references before entering the foreign predicate. PL_unify_term()
however may raise a resource exception for the global stack.
foreign_t pl_hello(term_t to) { char *s; if ( PL_get_atom_chars(to, &s) ) { return Sfprintf(Scurrent_output, "Hello \"%s\"\n", s); } else { term_t except; return ( (except=PL_new_term_ref()) && PL_unify_term(except, PL_FUNCTOR_CHARS, "type_error", 2, PL_CHARS, "atom", PL_TERM, to) && PL_raise_exception(except) ); } }
For reference, the preferred implementation of the above is below.
The
CVT_EXCEPTION
tells the system to generate an exception if
the conversion fails. The other CVT_
flags define the
admissible types and REP_MB
requests the string to be
provided in the current locale representation. This implies
that Unicode text is printed correctly if the current environment can
represent it. If not, a representation_error
is raised.
foreign_t pl_hello(term_t to) { char *s; if ( PL_get_chars(to, &s, CVT_ATOM|CVT_STRING|CVT_EXCEPTION|REP_MB) ) { return Sfprintf(Scurrent_output, "Hello \"%s\"\n", s); } return FALSE; }