[Haskell-cafe] Re: Fast Mutable Variables for the IO and ST monads

[Simon Marlow]

Bulat Ziganshin wrote:
> only for the souls interesting in writing efficient programs :)
> 
> i included in this letter my own module used for fast variables -
> "DataVariables.hs". and "wc.hs" contains example of using these vars.

The Var class is interesting - basically the equivalent of the MArray 
class for mutable variables.  Is there a reason you couldn't use the 
same pattern as the MArray class?  MArray of Ptr works fine, but for 
some reason you couldn't do it with Var, why not?

I suggest you follow the same scheme as the unboxed array types, and 
have IOURef/STURef types, parameterised over the element type.  Of 
course, we should have instances for all of the primitive numeric types 
plus Ptr, ForeignPtr, StablePtr, Bool.

Cheers,
	Simon