[Haskell-beginners] Identifying general patterns / typeclass instances

[yi huang]

I'm wondering how you gonna `append' two state ?

On Sat, Aug 6, 2011 at 6:14 PM, Tim Cowlishaw <tim at timcowlishaw.co.uk>wrote:

> Hi there all,
>
> I've come up with the following sketch for a simple agent-based
> simulation program in Haskell. However, I'd be interested in knowing
> whether there are any obvious instances of more general typeclasses
> hidden in there that I haven't recognised!
>
> https://gist.github.com/1129216
>
> Some explanation: A simulation is comprised of a starting state, and a
> set of agents which take in a state and output an updated state. The
> particular simulation I'm working on has very specific timing
> semantics in that, for each 'step' of the simulation, all the agents
> must see the same state (so they cannot simply be composed and applied
> sequentially), and the resulting states must be applied to create the
> next state in a well-defined order (hence the monoid restriction on
> the SimState type). For this reason, I'm having trouble coming up with
> a monad instance (which would seem to me to imply that the 'agent'
> functions would be applied sequentially). However, are there any other
> more general typeclasses that might offer useful abstractions in this
> case?
>
> In addition, the 'building up' of a simulation from an initial state
> also looks to me like an anamorphism of some kind - is this correct?
>
> Many thanks,
>
> Tim
>
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