[Haskell-cafe] Type systems preventing laziness-related memory leaks?
roma at ro-che.info
Fri Feb 20 09:13:17 UTC 2015
I'd be curious to see a (non-contrived) example.
On 20/02/15 09:05, David Feuer wrote:
> Probably not. There's real code that depends on the current foldl semantics.
> On Wed, Feb 18, 2015 at 10:40 AM, Joe Hillenbrand <joehillen at gmail.com> wrote:
>> Is foldl = foldl' ever going to happen?
>> On Tue, Feb 17, 2015 at 11:50 PM, Roman Cheplyaka <roma at ro-che.info> wrote:
>>> Note that foldr (+) 0 has nothing to do with laziness — it's eager. Its
>>> problem is that it's not tail-recursive.
>>> foldl (+) 0 would be an example of a laziness issue.
>>> If you want to specify which functions should or shouldn't be used in a
>>> lazy context, take a look at polarity (see Harper's Practical
>>> Foundations for Programming Languages). So you could say, for instance,
>>> that it doesn't make sense to use + in a lazy context; that'd eliminate
>>> half the cases of laziness-induced memory leaks in practice.
>>> If instead you want to impose some upper bound on the memory consumption
>>> without caring about specific cases, then see this ICFP'12 paper:
>>> On 18/02/15 07:04, Eugene Kirpichov wrote:
>>>> Hello haskell-cafe,
>>>> Let me repost here a question I posted to cstheory stackexchange - in
>>>> hopes that there are more type theory experts here.
>>>> Perhaps the main source of performance problems in Haskell is when a
>>>> program inadvertently builds up a thunk of unbounded depth - this causes
>>>> both a memory leak and a potential stack overflow when evaluating. The
>>>> classic example is defining sum = foldr (+) 0 in Haskell.
>>>> Are there any type systems which statically enforce lack of such thunks
>>>> in a program using a lazy language?
>>>> Seems like this should be on the same order of difficulty as proving
>>>> other static program properties using type system extensions, e.g. some
>>>> flavors of thread safety or memory safety.
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