[Haskell-cafe] Strange IO sequence behaviour (Was: sequence causing stack overflow on pretty small lists)
As an addendum to the recent discussion, can anyone explain why main crashes quickly with a stack overflow, whereas main' is happy to print "Hi" for ages (eventually crashing due to an out of memory condition)? bignum = 100 * 1000 * 1000 main = replicateM bignum (return ()) main' = replicateM bignum (putStrLn "Hi") Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange IO sequence behaviour (Was: sequence causing stack overflow on pretty small lists)
To give a very casual explanation, both mains are of the form "do this a bunch of times and return the results". Your first is "do nothing and return the ()s", but importantly, it has to execute all those nothings. Your second is "print hello a bunch and return the ()s". The list it wants to eventually return gets bigger and bigger as more prints happen, until poof! You should look at how replicateM works again, and hopefully it will make more sense with that in mind. On Sep 4, 2013 11:35 AM, "Tom Ellis" < tom-lists-haskell-cafe-2...@jaguarpaw.co.uk> wrote: > As an addendum to the recent discussion, can anyone explain why main > crashes > quickly with a stack overflow, whereas main' is happy to print "Hi" for > ages > (eventually crashing due to an out of memory condition)? > > bignum = 100 * 1000 * 1000 > main = replicateM bignum (return ()) > main' = replicateM bignum (putStrLn "Hi") > > Tom > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange IO sequence behaviour (Was: sequence causing stack overflow on pretty small lists)
Er, I seem to have misread and thought you were doing infinite replicateM, so that explanation doesn't completely address your question. That's what I get for reading on a phone! On Sep 4, 2013 4:11 PM, "Joe Q" wrote: > To give a very casual explanation, both mains are of the form "do this a > bunch of times and return the results". Your first is "do nothing and > return the ()s", but importantly, it has to execute all those nothings. > > Your second is "print hello a bunch and return the ()s". The list it wants > to eventually return gets bigger and bigger as more prints happen, until > poof! > > You should look at how replicateM works again, and hopefully it will make > more sense with that in mind. > On Sep 4, 2013 11:35 AM, "Tom Ellis" < > tom-lists-haskell-cafe-2...@jaguarpaw.co.uk> wrote: > >> As an addendum to the recent discussion, can anyone explain why main >> crashes >> quickly with a stack overflow, whereas main' is happy to print "Hi" for >> ages >> (eventually crashing due to an out of memory condition)? >> >> bignum = 100 * 1000 * 1000 >> main = replicateM bignum (return ()) >> main' = replicateM bignum (putStrLn "Hi") >> >> Tom >> >> ___ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange IO sequence behaviour (Was: sequence causing stack overflow on pretty small lists)
Ah, that's enlightening, and a good addition to http://ghc.haskell.org/trac/ghc/ticket/8189 On Sat 07 Sep 2013 04:31:31 JST, Tom Ellis wrote: > FYI, rwbarton on Reddit produced a nice answer: > > > http://www.reddit.com/r/haskell/comments/1luan1/strange_io_sequence_behaviour/cc32ec4 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange IO sequence behaviour (Was: sequence causing stack overflow on pretty small lists)
On Wed, Sep 04, 2013 at 04:35:17PM +0100, Tom Ellis wrote: > As an addendum to the recent discussion, can anyone explain why main crashes > quickly with a stack overflow, whereas main' is happy to print "Hi" for ages > (eventually crashing due to an out of memory condition)? > > bignum = 100 * 1000 * 1000 > main = replicateM bignum (return ()) > main' = replicateM bignum (putStrLn "Hi") FYI, rwbarton on Reddit produced a nice answer: http://www.reddit.com/r/haskell/comments/1luan1/strange_io_sequence_behaviour/cc32ec4 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
