Hi,
On Mon, May 17, 2010 at 08:49:35AM -0700, Jules wrote:
> The problem occurs in stateful objects when you receive an input and
> need to both modify your state and generate and deliver some output.
>
> I store my internal state in an atom and use swap! to update it,
> passing in the input and a pure function which accepts the object's
> current state and input and returns the object's new state.
I believe you need a ref for this, since you have to coordinate several
states: the object state and the input state.
(defn do-stuff
[state input]
(dosync
(let [[next-state output] (do-pure-stuff @state input)]
(ref-set state next-state)
output)))
or you combine both states in one, which might also make sense: the
current-state with the next input is a snapshot of your system from
which you can replay things.
(defn do-stuff
[state input]
(:output (swap! state do-pure-stuff input)))
Which is basically what you describe.
Sincerely
Meikel
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