[Haskell-cafe] Memory leak in infinite recursion

[winter]

Well, Yes, If the consumer side consume the result properly (not getting 
in the way of GC),  a space leak could be avoided.


On 2018年06月20日 18:54, David Feuer wrote:
> On Tue, Jun 19, 2018, 9:54 PM Dr.Koster <drkoster at qq.com 
> <mailto:drkoster at qq.com>> wrote:
>
>     In general infinite monadic recursion will leak, since the tail
>     position is always >> or >>= instead of your own recursive function
>
>
> That seems a bit strong. Monadic recursion *can* leak, but it need 
> not. >>= is typically lazy in its second argument, so it can produce 
> structure lazily. Consider the free monad, for example:
>
> data Free f a = Pure a | Wrap (f (Free f a))
>
> instance Functor f => Monad (Free f) where
>   Pure a >>= f = f a
>   Wrap ff >>= f = Wrap $ fmap (>>= f) ff
>
> See how we can produce Wrap without using f? As long as the base 
> functor isn't too large, this shouldn't leak.
>
>     , but under certain situations, e.g. IO without arguments, the
>     compiler will figure there's no need to push new stack frame. But
>     anyway it's better to checkout yourself rather relying on some
>     weak assumptions.
>
>     发自我的iPhone
>
>
>     ------------------ Original ------------------
>     *From:* Никита Фуфаев <kitttoran at gmail.com
>     <mailto:kitttoran at gmail.com>>
>     *Date:* Wed,Jun 20,2018 2:37 AM
>     *To:* haskell-cafe <haskell-cafe at haskell.org
>     <mailto:haskell-cafe at haskell.org>>
>     *Subject:* Re: [Haskell-cafe] Memory leak in infinite recursion
>
>     Hello everyone
>
>     In C you can't implement main loop with recursion like
>     void mainLoop() {
>       doSomething();
>       mainLoop();
>     }
>     because without optimisations stack will overflow.
>     In haskell it's common to write
>     mainLoop = doSomething >> mainLoop, and it doesn't leak memory
>     because of haskell's evaluation model.
>     Does memory leak or argument stack overflow happen in this case?
>     mainLoop = doSomething >> mainLoop >> exit ExitSuccess
>     What about this case?
>     mainLoopModeA = do
>       doSomething
>       when condition mainLoopModeB
>       mainLoopModeA
>     mainLoopModeB = do
>       doSomethingElse
>       when anotherCondition mainLoopModeA
>       mainLoopModeB
>
>     or this case?
>     mainLoopModeA = do
>     doSomething
>     if condition
>       then mainLoopModeB
>       else mainLoopModeA
>     mainLoopModeB = do
>     doSomethingElse
>     if anotherCondition
>       then mainLoopModeA
>       else mainLoopModeB
>
>     -- 
>     Nikita Fufaev
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