EXCEPTION-EXT Exception + extensions

These words implement an exception system in the widely known THROW & CATCH concept.

see the PFE-SIG wordset for catching OS traps.

CATCH ( xt -- 0|n )  
execute the given execution-token and catch any exception that can be caught therein. software can arbitrarily raise an exception using THROW - the value 0 means there was no exception, other denote implementation dependent exception-codes.

reference: p4_catch in ../src/xception.c:0040, export CO CATCH

THROW ( n -- )  
raise an exception - it will adjust the depth of all stacks and start interpreting at the point of the latest CATCH
if n is null nothing happens, the -1 (ie. FALSE ) is the raise-code of ABORT - the other codes are implementation dependent and will result in something quite like ABORT

reference: p4_throw in ../src/xception.c:0055, export CO THROW