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<  Advanced Erlang/OTP  ~  state machine (for a server)
Rechteck
Posted: Sat Mar 03, 2007 8:59 am Reply with quote
Joined: 03 Mar 2007 Posts: 2
First of all: Hello @ all!

Second: My Question:
What method shall I use to code a state machine?
Code:

client (Socket, State) ->
 case State of
  a ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_);
  b ->
   DoSomthingElse,
   client(Socket, SomeNewStateLike_a_);
 end,
or
Code:

client (Socket, State) when State == a ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_).

client (Socket, State) when State == b ->
   DoSomthingElse,
   client(Socket, SomeNewStateLike_a_).
The states are used for things like "login" "canplay" "play", i.e. the different states the server can be in. ("a" & "b" are obvioulsy just examples ;)
Or is there an even better way?

- Rechteck
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Mazen
Posted: Wed Mar 07, 2007 10:05 am Reply with quote
User Joined: 20 Jul 2006 Posts: 164 Location: London
Hi Rechteck,

First of all, you might want to consider looking at gen_fsm which is an implementation of a generic fsm (a behaviour). It should suite you perfectly. It can be found here: http://www.erlang.org/doc/doc-5.5.2/lib/stdlib-1.14.2/doc/html/gen_fsm.html

Now to answer your question. The second method is better. This is because of two reasons. 1) It is probably faster, and 2) The readability and structure of the code is far more comprehensive since it encapsulates the functionality of each state.

To consider...
Instead of writing
Code:

client (Socket, State) when State == a ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_)
....

Then patternmatch the State directly in the head:
Code:

client (Socket, a) ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_)
....

or if State is a record of many things:
Code:

client (Socket, #state{ state = a } = State) ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_)
....


But I really must say using gen_fsm for this helps alot Smile

Good luck Smile

Rechteck wrote:
First of all: Hello @ all!

Second: My Question:
What method shall I use to code a state machine?
Code:

client (Socket, State) ->
 case State of
  a ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_);
  b ->
   DoSomthingElse,
   client(Socket, SomeNewStateLike_a_);
 end,
or
Code:

client (Socket, State) when State == a ->
   DoSomething,
   client(Socket, SomeNewStateLike_b_).

client (Socket, State) when State == b ->
   DoSomthingElse,
   client(Socket, SomeNewStateLike_a_).
The states are used for things like "login" "canplay" "play", i.e. the different states the server can be in. ("a" & "b" are obvioulsy just examples Wink
Or is there an even better way?

- Rechteck
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Rechteck
Posted: Sun Mar 11, 2007 4:39 pm Reply with quote
Joined: 03 Mar 2007 Posts: 2
Many thanks!

- Rechteck
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