[boost] [msm] eUML guard/action location

Subject: [boost] [msm] eUML guard/action location
From: Christophe Henry (christophe.j.henry_at_[hidden])
Date: 2009-12-07 04:37:01

Hi Michael,

>What do you think about this instead?
>
>CurrentState() + cool_event()[Guard()]/(action()) = DestState()
>
>I think it more closely matches the UML syntax.

It's a good idea and it surely matches the UML syntax better. I think
the operator precedence will also work. There are however 2 issues:

- the current order "CurrentState() + cool_event()  = DestState()
[Guard()]/(action())" has been chosen to closely match the "normal"
row syntax. Only guard and action have been inverted because of
operator precedence.
- anonymous events. In this case, you have no event, so your syntax
would become:

CurrentState() [Guard()]/(action()) = DestState()

But now the guard/action are "attached" to the source state, which
means 2 grammars to support with the corresponding flow of compiler
risks and compile-time increases.

The first issue is only my worry that users would be confused (eUML
already being quite a change). I'd be interested to hear from others
about it.
The second issue is not so big that it's not worth a try.
I think I'll have a look at it and if it works we can then decide
which one we prefer.

Regards,
Christophe