wmb@MITCH.ENG.SUN.COM (Mitch Bradley) (01/19/91)
> : NCATCH ( cfa errno -- errno/0 ) > >R CATCH ( cfa errno -- retcode ) > R> OVER - ( retcode -- retcode errno=retcode ) > OVER AND IF ( retcode flag -- retcode ) > THROW > THEN > ; Since "0 THROW" is a no-op, the above reduces to: : NCATCH ( cfa errno -- errno/0 ) >R CATCH DUP R> - IF THROW THEN ; I think efficiency considerations for this function are down in the noise. > P.S.: Anyway, with the above code we have something similar to SETJMP.H C > library, but not SIGNAL.H. A generic Catch would provide both features in > one. See, SIGNAL.H can be implemented with SETJMP.H... Actually, signal handlers and CATCH/THROW are different things. A signal handler usually executes, does something, and then control returns to where it left off, as though nothing happened. To this end, the system signal handling mechanism has to create a new stack context for the handler, rather than going back to some previously- established context. However, it is sometimes useful to execute THROW from a signal handler, just as C signal handlers sometimes execute longjmp(). To this end, a good Forth signal handling implementation would probably create the "new" stack context on the stack of the task that receives the signal, so if the handler does a THROW, the signal handler stack will be automatically "deallocated". Actually, with the usual implementation of CATCH and THROW, it doesn't really matter where where put the signal handler stack; so long as you have set the user pointer to the right task (a necessity anyway), THROW will put you back in the right place. Mitch
bouma@cs.purdue.EDU (William J. Bouma) (01/20/91)
> : NCATCH ( cfa errno -- errno/0 ) > >R CATCH DUP R> - IF THROW THEN > ; You win! Sorry I brought it up. 8^( I am still gonna use variables for error numbers, though. -- Bill <bouma@cs.purdue.edu>
UNBCIC@BRFAPESP.BITNET (02/01/91)
Mitch, I think your implementation of TCATCH (NCATCH), that was small than
mine because 0 THROW is a do-nothing operation (is NOOP in ANS Forth? It
would be very useful for CFA's Tables...), was wrong. Unfortunely, I lost
your implementation. I think that there was an error because when CATCH
terminates succesfully (i.e. no 'true' THROWs), it returns 0.
(8-DCS)
Daniel C. Sobral
UNBCIC@BRFAPESP.BITNET
P.S.: I realized that your CForth has no Catch&Throw, although you claim
that it has error handling support; it's something like Catch&Throw?wmb@MITCH.ENG.SUN.COM (02/04/91)
Daniel Sobral just convinced me of the error of my ways. His implementation of "tagged CATCH" is correct, and my "simplification" of his implementation is incorrect. Embarrassed, Mitch Bradley, wmb@Eng.Sun.COM