[Haskell-cafe] Re: hmatrix

Alberto Ruiz aruiz at um.es
Thu Jun 5 11:16:09 EDT 2008

Hello Bulat and Anatoly,

I have written a first version of an interface to inplace updates in the 
ST monad for the hmatrix vectors and matrices. Many things must be
improved (range checking, documentation, etc.) but I hope that the 
general idea makes sense.

A few usage examples:





Any suggestion will be welcome. I'm impressed by the power of the ST 
monad, it is extremely useful and elegant. Thank you again for your help!

In the future I will also try to include efficient conversions to/from 
standard Haskell arrays and those of other related libraries like Jed 
Brown's CArray.



Bulat Ziganshin wrote:
> Hello Alberto,
> Tuesday, June 3, 2008, 12:56:50 PM, you wrote:
>> Good! So you can easily "hide" the IO operations in the ST monad. I will
>> definitely look into it.
> from implementation POV ST monad is nothing but renamed IO monad which
> exports only subset of its operations which are guaranteed to safe.
> or, saying in other words, it's just type hackery around IO monad that
> provides safe operations
> it's possible to define ST monad and its operations as following:
> newtype ST s a = forall s. ST_Constructor (IO a)
> unsafeIOtoSt action = ST_Constructor action
> runST (ST_Constructor action) = unsafePerformIO action
> newtype STRef s a = forall s. STRef (IORef a)
> readSTRef (STRef ref)  =  unsafeIOtoSt (readIORef ref)
> and so on. GHC uses technically (but not ideologically!) different
> implementation where both monads are specializations of one generic
> type. while Hugs afair uses exactly this approach. you may also look
> at ArrayRef lib which reimplements arrays/refs for both compilers in
> more unified way
> anyway, because ST is just IO monad modulo type tricks, you can
> execute any IO action inside ST by lifting it with unsafeIOtoSt

More information about the Haskell-Cafe mailing list