July 2015 - Haskell-Cafe

[GHC 7.8.4] IO Monad leak space?
by Baojun Wang 09 Jul '15

09 Jul '15

Hi, First of all, I found it interesting that loopM_ f k n s = when (k <= n) (f k >> loopM_ f (s+k) n s) loopM_ seems faster than mapM_ ( mapM_ f [k, k+s..n])) I think mapM_ is used very commonly, why it's performance is even lower than a hand-written loop function? 2nd, even I replace mapM_ with loopM_ from above, when chain IO action, it still can leak space. ( Because IO Monad (>>) need keep ``RealWorld s'' updated so that I/O actions can be done in-order? ) Consider below function: f3 :: UArray Int Int -> IOUArray Int Int64 -> Int -> IO () f3 u r i = let !v = u ! i in go (f31 v) i i where f31 v j = readArray r j >>= \v1 -> writeArray r j (v1 + (fromIntegral i) * (fromIntegral v)) f31 :: Int -> Int -> IO () go g k s = when (k <= maxn) ( g k >> go g (s+k) s ) When call f3: loopM_ (f3 uu res) 1 1 1000000 Which will have blow profiling output: individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc ... loopM_ Main 104 4000002 7.4 10.1 100.0 99.3 f3 Main 113 1000000 1.0 2.0 70.2 69.1 f3.go Main 116 14970034 32.7 67.1 68.8 67.1 f3.f31 Main 117 13970034 34.5 0.0 36.1 0.0 f3.f31.\ Main 118 13970034 1.7 0.0 1.7 0.0 f3.f31 Main 114 0 0.3 0.0 0.4 0.0 f3.f31.\ Main 115 0 0.1 0.0 0.1 0.0 ... Why f3.go consumes so much space (67.1%)? The only reason I can think of is IO Monad chain (>>) isn't space free as I thought. Did I get something fundamentally wrong? Thanks baojun

6 14

Problems with type families
by Leza Morais Lutonda 09 Jul '15

09 Jul '15

Hi All! Consider the following definitions: type family TFunIn t e type family TFunOut t e data IdT data ComposeT t1 t2 -- etc... type instance TFunIn (ComposeT t1 t2) e = TFunIn t2 e type instance TFunOut (ComposeT t1 t2) e = TFunOut t1 e -- etc... class SignalT t e where transform :: t -> TFunIn t e -> TFunOut t e instance (SignalT t1 e, SignalT t2 e) => SignalT (ComposeT t1 t2) e where transform _ x = (transform (undefined :: t1) . transform (undefined :: t2)) x Due to the `TFunIn` and `TFunOut` type families instances for [(ComposeT t1 t2) e], the `transform` function for [(ComposeT t1 t2) e] instance of SignalT should be inferred as: transform :: t -> TFunIn (ComposeT t1 t2) e -> TFunOut (ComposeT t1 t2) e <==> :: t -> TFunIn t2 e -> TFunOut t1 e But I cannot figure out why it does not compile. Any ideas? Thanks. -- Leza Morais Lutonda, Lemol-C http://lemol.github.io 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964 http://cujae.edu.cu

2 7

You know, I am tired of it.
by Stefan Reich 08 Jul '15

08 Jul '15

Whatever "community" I go, they all pretend like their old shit is SO important.

9 15

The evil of "mailing list removals" - and Microsoft-sponsored s**t ^^
by Stefan Reich 08 Jul '15

08 Jul '15

3 2

List Moderation
by Gershom B 08 Jul '15

08 Jul '15

Stefan Reich has been removed as a member from this list due to a stream of unapologetically off-topic posts. Best, Gershom

4 3

[Haskell-cafe] tinybrain.blog.de/2015/07/08/the-evil-of-mailing-list-removals-20645305/
by Stefan Reich 08 Jul '15

08 Jul '15

1 0

They scrubbed my link??
by Stefan Reich 08 Jul '15

08 Jul '15

1 0

Announcing: monadic FRP using stm
by Silvio Frischknecht 08 Jul '15

08 Jul '15

Hi Haskellers, I know there are already a lot of FRP libraries out there, but still. This is my take on it. It's a very simple library. There are portable Signals that are basically TVars with some update Notifiers. Then you can combine them using a continuation like monad. Because you have a Monad and not only Applicative it's very intuitive and powerful. Check it out. github: https://github.com/yokto/Updater hackage: https://hackage.haskell.org/package/Updater Be warned though. There are probably still some bugs around, but the basics seem to work and there is an example program. Silvio

2 4

The Internet is insane
by Stefan Reich 08 Jul '15

08 Jul '15

They thumb up the shit and destroy the good stuff. I am really, seriously, interested how anyone can even try to explain how JavaX is supposedly worse (??) than Java. Cheers

1 0

Request for maintainer(s) : language-javascript / hjsmin
by Alan & Kim Zimmerman 08 Jul '15

08 Jul '15

Hi all I am the author of language-javascript and its companion hjsmin. Unfortunately I do not use the libraries myself, and I am falling behind in maintaining them, all the more so with the new ECMASCRIPT spec out. So I am calling for volunteers to take over maintenance of these two packages. Regards Alan

4 8