[m-dev.] Pure Functional throwing exception

[Julien Fischer]

Hi,

On Tue, 7 May 2019, Barthwal wrote:

> Can a pure function throw exceptions?

In Mercury, yes.

> I don't plan to catch these functions in pure function.

If you wanted to, you could.  (Although doing so may affect
the determinism for your function.)

> But if something illegal happens, I want to send a message like:
> 
> throw error("Some Message")

Assuming you don't catch the exception within your program, the
runtime's uncaught exception handler will print the exception out when
the exception propagates back past main/2.   (It may also print a stack
trace if you're using a grade that records that information.)

As a general rule, I would recommend not throwing strings about.  The
library has a builtin type named software_error/1 which is suitable for
exceptions where something illegal happens.

Julien.