[Haskell-cafe] Type systems preventing laziness-related memory leaks?
david.feuer at gmail.com
Fri Feb 20 07:05:50 UTC 2015
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.
>> > http://cstheory.stackexchange.com/questions/29518/type-systems-preventing-laziness-related-memory-leaks
>> > 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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