> Here is yet another solution, using objects, which actually combines
> Zheng's and Oleg's ideas. That is, it separates state and function,
> but provides only access to state through a cloning method, so that it
> is completely type safe. This is just what objects are good at!
>
> class ['a,'b] arrow (f : 'a -> 'b) =
>   object (self) method call = f method copy = self end

Yet another nice solution I would never have imagined :-)

And the performance is quite good :

1.428032 microseconds on my small benchmark

(the unsafe Ref implantation takes 0.75 microseconds while the CPS
implantation takes 2.7 microseconds).

Nevertheless, I have carried out my benchmark on Oleg's implementation
and find an impressive performance :

0.74 microseconds !

Now, I will re-write my combinators and see which style better suits my needs.

Thanks,

-- 
Pierre-Evariste DAGAND
http://perso.eleves.bretagne.ens-cachan.fr/~dagand/