[erlang-questions] Exceptions in guards are blocked. Why?

[Richard O'Keefe]

On 30 Jan 2009, at 2:14 am, Alexander Semenov wrote:

> Hi, folks,
>
> Can you explain me why exceptions are blocked in guards?

It is not that exceptions are *blocked* in guards,
but that they signify *failure*.

> For example I wrote this in erlang shell:
>
> F = fun(X) when (X == 0) or (X / 0 > 2) -> true; (_) -> false end.

Why did you write that rather than
	F = fun (X) -> X == 0 orelse X/0 > 2 end

> Is this cause of 'side effects free' guards nature?

Not really.  It's because guards aren't true or false;
they succeed or fail.  (Blurring this distinction was a
really bad idea.)