Exception Handling? Impossible!

[richw at ada-uts.UUCP]

Sorry if this is getting boring, but...

I fixed a bug; a "raise" occuring before a "Begin" is encountered
works as one would expect now.  I also made things a little more
space efficient.  Otherwise, the macros' behavior hasn't changed.

Also, note that the environment stack has a fixed depth -- this can
be changed (at the expense of more procedure calls) by having pushed
environments be allocated from the heap (i.e. use malloc).

The updated exceptions.{c,h} follow:

-----------------------  exceptions.h  ----------------------------
#include <setjmp.h>

typedef char *Exception;

extern jmp_buf _env_stack[];
extern int _env_index, _bad_index;
extern Exception _exc;

#define Begin { if (_env_index == _bad_index) _env_overflow();\
		if (!setjmp(_env_stack[_env_index++])) {

#define Except      _env_index--;

#define When(e) } else if (_exc == e) {

#define Others  } else if (1) {
			
#define End     } else _unhandled(); }

#define raise(e) (_exc = e,\
                  (_env_index == 0)\
		       ? _unhandled() :\
		       longjmp(_env_stack[--_env_index],1) )

---------------------------  exceptions.c  ----------------------------
#include <setjmp.h>
#include <stdio.h>

#define BELL '\007'   /*  ASCII control-G  */

#define STACK_SIZE 101

jmp_buf _env_stack[STACK_SIZE];
int _env_index = 0;
int _bad_index = STACK_SIZE;
char *_exc;

_unhandled()
{
    fflush(stdout);
    putc(BELL, stderr);
    fprintf(stderr, "\nUnhandled Exception: %s\n", _exc);
    exit(1);
}

_env_overflow()
{
    fflush(stdout);
    putc(BELL, stderr);
    fprintf(stderr, "\nException handlers nested too deeply");
    fprintf(stderr, "\nMaximum is %d\n", STACK_SIZE - 1);
    exit(1);
}