Hello Gracjan, Tuesday, June 07, 2005, 4:52:50 PM, you wrote:
a=:b = writeIORef a b
GP> Pretty shame := is already reserver :(. := reserved for infix data constructors, as any other symbols starting with ':' GP> As I see this could be generalized to all Ref-like constructs GP> (IO,ST,others?) i think so
a+=b = modifyIORef a (\a-> a+b) a-=b = modifyIORef a (\a-> a-b) a=::b = ((a=:).b) =<< val a GP> Is this convoluted modify? Why doesn't it use modifyIORef? Or am I wrong?
a=::(*2) doubles value of `a` and so on. i don't define this as `modifyIORef` equivalent just because it's is a funnier definition :) also i was interested to define all funcs via 2 primitives - `val` and '=:` (which is like readRef/writeRef in your example); such definitions will be more convenient for defining Ref as class: class Ref a where val .... (=:) ... instance Ref (MVar a) where val=takeMVar (=:)=putMVar where all other operations are defined via this two primitives. of course, it's not the best way - adding `modifyRef` to Ref class with default definition via 'val' and `=:' would be better
newList = ref [] list <<= x = list =:: (++[x]) GP> Is this append?
it is adding one value to end of list, for Chan'nels it would be `writeChan` GP> Haskell as ultimate imperative language :) it may be better, though :)
I use this module to simplify working with references in my program. The first inteface can be used for IORef/STRef/MVar/TVar and second for lists and Chan
GP> Then we should create classes for those interfaces. of course. i don't done it only because my own program use only IORefs with help of this defines my code was significantly lightened. see for example: crc <- ref aINIT_CRC origsize <- ref 0 let update_crc (DataChunk buf len) = do when (block_type/=DATA_BLOCK) $ do crc .<- updateCRC buf len origsize += toInteger len ..... acrc <- val crc >>== finishCRC aorigsize <- val origsize you can imagine how this code looked before, using newIORef, readIORef and so on... ('.<-' is `modifyIORef` in IO monad) but of course i will prefer more direct support of imperative programming. i have some proposal - translating x := @x + @y + @@f 1 2 to x1 <- val x y1 <- val y f1 <- f 1 2 x =: x1+y1+f1 but i guess that number of True Imperative Programmers among GHC users is not very large :) in any case, there is an interesting STPP array indexing preprocessor (http://www.isi.edu/~hdaume/STPP/stpp.tar.gz), which decides nearly the same problem -- Best regards, Bulat mailto:bulatz@HotPOP.com