in reply to Are state machines just for parsing?

Why doesn't the simple-minded method work? 
#!/usr/bin/perl -w

# State transition table
#
#      Current   Inputs      Next    Action
$next{'initial'}{'left' } = ['red',  sub { print "Red \n"} ];
$next{'initial'}{'right'} = ['blue', sub { print "Blue\n"} ];
$next{'red'}    {'left' } = ['blue', sub { print "Blue\n"} ];
$next{'red'}    {'right'} = ['end',  sub { print "End \n"} ];
$next{'blue'}   {'left' } = ['blue', sub { print "Blue\n"} ];
$next{'blue'}   {'right'} = ['red',  sub { print "Red \n"} ];
$next{'end'}    {'left' } = ['end',  sub { print "End \n"} ];
$next{'end'}    {'right'} = ['end',  sub { print "End \n"} ];

@arbitrary_inputs = qw/left left right left left right right left/;

$state = 'initial';
for (@arbitrary_inputs)
{
    $action = $next{$state}{$_}->[1];
    $action->();
    $state  = $next{$state}{$_}->[0];
}

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-- All code is 100% tested and functional unless otherwise noted.

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Re^2: Are state machines just for parsing?
by samtregar (Abbot) on Dec 08, 2004 at 02:55 UTC
    Well, first off because my problem doesn't have states with just one possible next state, it has a set. Sure I could enhance your example until it could handle a fully generalized state machine. Then I could find a good name and put our solution on CPAN. But if there's already a solution out there I can use, wouldn't it be better to use that?

    -sam

[reply]
      But if there's already a solution out there I can use, wouldn't it be better to use that?
      See also: Abstraction Inversion.
[reply]
Re^2: Are state machines just for parsing?
by sleepingsquirrel (Chaplain) on Dec 08, 2004 at 16:47 UTC
    It occured to me that it might be beneficial to show the state transition diagram for the above state machine. 
    
 +--------------------------------------------------+
 |                                                  |
 |                       _______                    |
 |                 left /       \ right             |
 |         +------------|initial|-----------------+ |
 |         |            \_______/                 | |
 |         |                                      | |
 |         |                          +--------+  | |
 |      ___V___                       |        |  | |
 |left /       \ right                |       _V__V_V_ 
 +-----|  red  |--------------+       | left /        \ right
       \_______/              |       +------|  blue  |------+
           ^                  |              \________/      |
           |                  |                              |
           |                  |                              |
           |                __V____                          |
           |          left /       \ right                   |
           |         +-----|  end  |------+                  |
           |         |     \_______/      |                  |
           |         |       ^  ^         |                  |
           |         |       |  |         |                  |
           |         +-------+  +---------+                  |
           |                                                 |
           +-------------------------------------------------+

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    -- All code is 100% tested and functional unless otherwise noted.
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