Big state machines

Bjarne Däcker <>
Wed Apr 20 10:51:39 CEST 2005


I believe that SDL was originally defined
to describe hardware units similar to a 
coffee machine. A typical input would
be a button pressed. It has either immediate 
effect or if it comes in a state where it is 
irrelevant it will be ignored.

Bjarne

----- Original Message ----- 
From: "Vance Shipley" <>
To: "Ulf Wiger" <>
Cc: <>
Sent: Tuesday, April 19, 2005 4:17 PM
Subject: Re: Big state machines


> On Tue, Apr 19, 2005 at 06:54:18AM +0200, Ulf Wiger wrote:
> }  
> }  I may read your message wrong, but the problem with the UML approach
> }  is that you cannot easily say, for a given state: "match these
> }  expected messages, but implicitly refer any other message". This
> }  is the semantics needed for all transient states, since a transient
> }  state may _never_ discard a message it doesn't recognize.
> 
> I don't know UML, and maybe never will as you've told us it isn't
> very helpful in Erlang.  :)
> 
> In SDL an unspecified signal is implicitly handled by consuming it
> and transitioning back to the current state.  My point was that this 
> default behaviour is important to have.
> 
> - - - -




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