Re: [boost] [fsm review] Terminal emulator example

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2008-08-18 23:52:03

Phil Endecott wrote:
> Andrey Semashev wrote:
>> Phil Endecott wrote:
>>> Dear All,
>>>
>>> Here's another FSM example which I hope is a bit less trivial than the
>>> last one.  It's for the escape sequence handling in a terminal
>>> emulator.
> 
>>> My view is that the ad-hoc version of the code is sufficiently readable
>>> and efficient for my needs, and that the Boost.FSM version does not
>>> improve on it.
>>
>> Actually, the ad-hoc code is a good example for what is known as
>> spagetti-style
> 
> Can you elaborate on why you say that?  To me, "spagetti" code is code
> where the flow-of-control goes all over the place in a complex and not
> easily discernible pattern.  In my "ad-hoc" implementation, the main
> flow-of-control is contained in a single function which all fits on the
> screen at the same time and has if and switch statements nested at most
> 4 deep.

Exactly, that's why I call it spagetti. I'm easily lost in all these
conditions in the function and, since the function is not complete, I
would expect the function to be much bigger than the screen.

> If it's the depth of nesting that you dislike it could easily
> be flattened like this:

Better, but not as good as I'd like to. The code is getting close to
what I have presented, and in the end it would become quite similar,
except for that switch-case across states in your code would be
equivalent to the FSM in mine.

>> Below is an improved version of the
>> terminal, with corrected mistakes and categorized events.
> 
> A couple of questions:
> - Does it correctly handle digits in normal mode?

Yes. Since "digit" derives from the "printable_char", digits go into
"on_process(printable_char const&)".

> - How can I access the screen and cursor position from outside? (Or, if
> I can't access the content of the states from outside, how can I access
> an externally-stored screen and cursor from inside the states?)

Yes, you can access any state or its base through the "get" method:

    m_FSM.get< Common >().screen;