# News aggregator

### Can you explain this?

Launch ghci

Enter this number https://gist.github.com/eccstartup/382579e0a4ef9133eb16 1312414124532675478362532543571329085712389578957198523598236057236457230478923749028357328974892375829037589230748923569823604327894723589072389547328957238907523895789207589230758932758903274892305692803567892037145892137580927389573289475238956729803659028375892037698023716891205237509812759807589263108972589236589237489326589325790238502156728013523809759823

Enter it^2 for 9 times

I get a Bus error: 10.

I use ghcformacosx, with version 7.10.1 in Yosemite. I notice that not all really large numbers can reproduces this, but this one can cause bus error again and again, even after a restart. I admit that this number is typed randomly if you want to know how I get it. What could be the reason?

submitted by eccstartup[link] [21 comments]

### When is sequenceA an applicative morphism?

Suppose T is traversable and applicative, and F is applicative. We have the map

sequenceA :: T (F a) -> F (T a)which I'd like to think of as a natural transformation TF -> FT. If you like we can be explicit about this by writing

sequenceC :: Compose T F a -> Compose F T a sequenceC = Compose . sequenceA . getComposeSince F and T are applicative, Compose F T and Compose T F are as well. When is it the case that sequenceC satisfies the following equations?

sequenceC . pure = pure sequenceC (f <*> x) = sequenceC f <*> sequenceC xI suspect the first equation always holds, so I'm more interested in the second.

The second equation often fails. For example, for T = Maybe, F = (,) String:

f :: Compose Maybe ((,) String) (a -> Bool) f = Compose $ Just ("a", \_ -> True) x :: Compose Maybe ((,) String) a x = Compose Nothingand we have

sequenceC (f <*> x) == Compose ("", Nothing) sequenceC f <*> sequenceC x == Compose ("a", Nothing)As another example, it holds if we take T = (,) String and F = Maybe.

submitted by seriousreddit[link] [3 comments]

### [PDF] Invertible Syntax Descriptions: Unifying Parsing and Pretty Printing

### Haskell logo Keycaps finally up for group-buy

So, we did it! The Haskell Keycap group-buy is finally up! See it here: http://www.pimpmykeyboard.com/deals/haskell-logo-keycaps/?nowforsale

Note that you'll initially be charged the 'full' amount, though you'll be refunded if we get more than 50, 75, 100, or 250 keys!

There is also a sub-deal for 1x (normal size), whereas the main deal is for a 1.25x (OS key).

submitted by NFATracker[link] [5 comments]

### Last CFP Bx'15: 4th International Workshop onBidirectional Transformations

### stitch: a tiny css dsl for haskell

### Monoid instance for Either that mappends both sides

Does something like this exist somewhere already?

newtype EitherMonoids a b = EitherMonoids (Either a b) deriving (Show) instance (Monoid a, Monoid b) => Monoid (EitherMonoids a b) where mempty = EitherMonoids $ Right mempty (EitherMonoids (Left xs)) `mappend` (EitherMonoids (Left ys)) = EitherMonoids $ Left $ xs `mappend` ys (EitherMonoids (Right xs)) `mappend` (EitherMonoids (Right ys)) = EitherMonoids $ Right $ xs `mappend` ys x@(EitherMonoids (Left _)) `mappend` (EitherMonoids (Right _)) = x (EitherMonoids (Right _)) `mappend` x@(EitherMonoids (Left _)) = x submitted by singpolyma[link] [11 comments]

### skip hpc during build

### runghc and GhcWithInterpreter

### Proposal for a generic showIntAtBase

### A Random Strawman

### immortal profiling

### New gtk2hs 0.12.4 release

Thanks to John Lato and Duncan Coutts for the latest bugfix release! The latest packages should be buildable on GHC 7.6, and the cairo package should behave a bit nicer in ghci on Windows. Thanks to all!

~d