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:
http://perception.inf.um.es/~aruiz/darcs/hmatrix/examples/inplace.hs
Code:
http://perception.inf.um.es/~aruiz/darcs/hmatrix/lib/Data/Packed/ST.hs
http://perception.inf.um.es/~aruiz/darcs/hmatrix/doc/html/Data-Packed-ST.html
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.
Thanks,
Alberto
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
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