Re: [Ocaml-lib-devel] Exceptions considered harmful

[Brian H. <bh...@sp...>]

On 29 Jun 2004, skaller wrote:

> In general, I think exceptions are a bad idea.
> I spend a lot of time removing them from my code :(

Looking at your examples, I think you're trying to fix something that 
doesn't need fixing.  My general rule is "don't catch exceptions that you 
don't know how to handle".  The default handling of uncaught exceptions 
isn't perfect, but it's orders of magnitude better than most program's 
error handling, and I can't think of a better way to handle things.  Or, 
to put it a different way, exceptions are the worst possible way to handle 
errors, except for all the other ways.

Certainly, quietly discarding exceptions is a real bad idea.  Code like:
	try
		...
	with
		| _ -> ()
is evil.  Dropping certain exceptions, yes.  But all exceptions?

As for the theoretical foundations, I wouldn't be surprised if someone who 
follows the theory comes back with actual citations.  I don't think the 
theoretical foundations would be that hard- exceptions are just an 
alternate return path.  Actually, I go all types of expressions can be one 
of two things- either an exception or the unexceptional type.  Then I 
start defining my basic operators to properly "pass along" an exception.  

So, for example, an if statement of the form "if expr1 then expr2 else 
expr3" would be evaluated like this:
	- if expr1 evaluates to an exception e, the entire expression
	  evaluates to that exception
	- if expr1 evaluates to true, the expression evaluates to
	  whatever expr2 evaluates to (this can be an exception)
	- if expr1 evaluates to false, the expression evaluates to
	  whatever expr3 evaluates to.

This keeps me firmly within strongly typed territory, as I understand 
things.  Compared to monads, this is pretty trivial.

-- 
"Usenet is like a herd of performing elephants with diarrhea -- massive,
difficult to redirect, awe-inspiring, entertaining, and a source of
mind-boggling amounts of excrement when you least expect it."
                                - Gene Spafford 
Brian