[Haskell-cafe] class Ref...
bulatz at HotPOP.com
Tue Jun 7 12:22:28 EDT 2005
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
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
instance Ref (MVar a) where
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
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
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
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
Bulat mailto:bulatz at HotPOP.com
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