Hi, Better late than never... ;-)
Neil Jerram <[EMAIL PROTECTED]> writes: > Another (lesser) problem with lazy-catch and with-exception-handler is > that they are always used in practice in a particular pattern. For > lazy-catch the pattern is > > (catch tag > (lambda () > (lazy-catch tag thunk lazy-handler)) > catch-handler) > > For with-exception-handler the pattern (as shown by all the examples > in SRFI-34) is > > (call/cc > (lambda (k) > (with-exception-handler > (lambda (obj) > ... > (k 'exception)) > thunk))) > > Why is this a problem? Because it strongly suggests that these forms > are more general than is useful. And there is a cost to this: a bit > more typing in Scheme, and in the case of Guile a lot more complexity > in the C code needed to set up a catch and lazy catch pair (which is > relevant to the backtrace problem). OTOH, this would suggest that `lazy-catch' and `call/cc' are all we need to implement `catch'. This is probably the reason why SRFI-34 defines no construct equivalent to `catch'. >From a theoretical viewpoint, it seems to me that it would make sense to just keep `lazy-catch' as a primitive and have `catch' implemented as a macro on top of it. Now, from Guile's implementation viewpoint, I guess it would be much more costly/complex as you said. Anyway, thanks for your patch: it's nice to see this issue is going to be fixed! ;-) And sorry for not replying earlier. Ludovic. _______________________________________________ Guile-devel mailing list Guile-devel@gnu.org http://lists.gnu.org/mailman/listinfo/guile-devel
