[Haskell-cafe] return with mutable object

[Baojun Wang]

Thanks a lot for the correction, I guess the right identity law would be
violated, right? I was think about the type constructor stuff, next time
should definitely think about the laws first.

On Tuesday, June 17, 2014, Bob Ippolito <bob at redivi.com> wrote:

> Your understanding is not correct. The monad laws would be violated If
> return did make a new mutable object.
> http://www.haskell.org/haskellwiki/Monad_laws
>
> Side-effects typically have a `m ()` return type, so your "more Haskell"
> way is not idiomatic Haskell.
>
>
>
> On Tue, Jun 17, 2014 at 7:53 PM, Baojun Wang <wangbj at gmail.com
> <javascript:_e(%7B%7D,'cvml','wangbj at gmail.com');>> wrote:
>
>> To make my question more clearer, will test1/test2 have noticeable
>> performance difference?
>>
>> -- mutable1.hs
>>
>> import qualified Data.Vector.Mutable as MV
>>
>> import Control.Monad
>>
>> import Control.Monad.Primitive
>>
>> a1 :: (PrimMonad m) => MV.MVector (PrimState m) a -> m ()
>>
>> a1 v = do
>>
>>   -- do something
>>
>>   return ()
>>
>> a2 :: (PrimMonad m) => MV.MVector (PrimState m) a -> m ()
>>
>> a2 v = do
>>
>>   -- do something else
>>
>>   return ()
>>
>> b1 :: (PrimMonad m) => MV.MVector (PrimState m) a -> m (MV.MVector
>> (PrimState m) a)
>>
>> b2 :: (PrimMonad m) => MV.MVector (PrimState m) a -> m (MV.MVector
>> (PrimState m) a)
>>
>> b1 v = do
>>
>>  -- do something different
>>
>>  return v
>>
>> b2 v = do
>>
>>  -- do something else different
>>
>>  return v
>>
>> test1 :: IO ()
>>
>> test1 = do
>>
>>  v1 <- MV.replicate 1000 0
>>
>>  a1 v1
>>
>>  a2 v1
>>
>>  return ()
>>
>> test2 :: IO ()
>>
>> test2 =
>>
>>  MV.replicate 1000 0 >>= b1 >>= b2 >> return () -- I'd prefer this way
>> cause it's more haskell.
>>
>>
>>
>>
>> On Tue, Jun 17, 2014 at 5:50 PM, Baojun Wang <wangbj at gmail.com
>> <javascript:_e(%7B%7D,'cvml','wangbj at gmail.com');>> wrote:
>>
>>> Hi List,
>>>
>>> Per my understanding, return x would make a new copy of the object. What
>>> if the returned object is mutable? Will this make a new (mutable) object?
>>>
>>> My concern is if I created a very large mutable object, does return
>>> mutable make a full copy of the original mutable data, or just copy a
>>> reference (pointer?)?
>>>
>>> Thanks
>>> baojun
>>>
>>
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe at haskell.org
>> <javascript:_e(%7B%7D,'cvml','Haskell-Cafe at haskell.org');>
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20140617/f26376da/attachment.html>