Re: [Haskell-cafe] mapFst and mapSnd

On Thu, May 30, 2013 at 7:12 PM, Shachaf Ben-Kiki wrote: > One generalization of them is to lenses. For example `lens` has > "both", "_1", "_2", such that "mapPair = over both", "mapFst = over > _1", etc., but you can also get "fst

Re: [Haskell-cafe] mapFst and mapSnd

On Tue, May 28, 2013 at 1:54 AM, Dominique Devriese wrote: > Hi all, > > I often find myself needing the following definitions: > > mapPair :: (a -> b) -> (c -> d) -> (a,c) -> (b,d) > mapPair f g (x,y) = (f x, g y) > > mapFst :: (a -> b) -> (a,c) -> (b,c) > mapFst f = mapPair f id > > ma

[Haskell-cafe] Haskell + RankNTypes + (forall p. p Char -> p Bool) sound?

I was trying to figure out a way to write absurd :: (forall p. p Char -> p Bool) -> Void using only rank-n types. Someone suggested that Haskell with RankNTypes and a magic primitive of type (forall p. p Char -> p Bool) might be sound (disregarding the normal ways to get ⊥, of course). Is that tru

Re: [Haskell-cafe] quotRem and divMod

On Mon, Jan 28, 2013 at 4:27 PM, Artyom Kazak wrote: > Hi! > > I’ve always thought that `quotRem` is faster than `quot` + `rem`, since both > `quot` and `rem` are just "wrappers" that compute both the quotient and the > remainder and then just throw one out. However, today I looked into the > impl

[Haskell-cafe] Taking over ghc-core

With Don Stewart's blessing (), I'll be taking over maintainership of ghc-core, which hasn't been updated since 2010. I'll release a version with support for GHC 7.6 later today. Shachaf ___ Has

Re: [Haskell-cafe] Smarter do notation

On Sat, Sep 3, 2011 at 19:34, Daniel Peebles wrote: ... > Of course, the fact that the return method is explicitly mentioned in my > example suggests that unless we do some real voodoo, Applicative would have > to be a superclass of Monad for this to make sense. But with the new default > supercla

Re: [Haskell-cafe] Interactive chatbot

On Wed, Nov 4, 2009 at 3:14 PM, Jason Dagit wrote: > > > On Wed, Nov 4, 2009 at 2:21 PM, Torsten Otto wrote: >> >> Hi! >> >> My students have the task to program an interactive chatbot. We have run >> into a problem that I can't solve either: >> >> When we read the user's input through >> >   t <

[Haskell-cafe] LinuxFest Northwest 2009

LFNW 2009 () is going to be at the end of April, and I was wondering if anyone here is going to be there, or possibly a Haskell-related presentation. Last year I met ac from #haskell there, but it would be nice if more people came, especially with the (relatively) b

Re: [Haskell-cafe] Sequencing Parsers: a Simple Example

> Hi > (>>=) :: Parser a -> Parser b -> Parser b > p >>= f = \inp -> >case p inp of > [] -> [] > [(v, out)] -> parse (f v) out > based on a lot of guesswork, after the mess created by the OCR, I > managed to get the above example to work syntactically but is it > semantically correct?

Re: [Haskell-cafe] Best way to format a number

On Nov 20, 2007 7:07 PM, Don Stewart <[EMAIL PROTECTED]> wrote: > You can work around it for now with: > > Prelude Text.Printf> printf "%02d\n" 3 >> return () > 03 It may be simpler to specify the type explicitly: Prelude Text.Printf> printf "%02d\n" 3 :: IO () 03 Shachaf ___

Re: [Haskell-cafe] What is the role of $!?

On Nov 14, 2007 4:27 PM, Justin Bailey <[EMAIL PROTECTED]> wrote: > It's: > > f $! x = x `seq` f x > > That is, the argument to the right of $! is forced to evaluate, and > then that value is passed to the function on the left. The function > itself is not strictly evaluated (i.e., f x) I don't b

Re: [Haskell-cafe] Type inference problem with division (/)

On 10/30/07, Tim Chevalier <[EMAIL PROTECTED]> wrote: > On 10/30/07, noa <[EMAIL PROTECTED]> wrote: > > > > Hi! > > > > I have the following function: > > > > theRemainder :: [String] -> [String] -> Double > > theRemainder xs xt = sum( map additional (unique xs) ) > > where > > addi

Re: [Haskell-cafe] Defining new operators

> Hi all, > > Given the follwing function: > > > owner :: Step -> Scenario > > owner (Step id scenario action state response) = scenario > > Is it possible to define the owner function in such way that I can write > x.owner (returning the scenario related with the Step x)? Some people use (|>), w

Re: [Haskell-cafe] Is this haskelly enough?

For the monadically-challenged, this is equivalent, yes-no? maxsubarrays = maximumBy (compare `on` sum) . concat . (map tails) . inits Or: maxsubarrays = maximumBy (compare `on` sum) . concatMap tails . inits (>>=) for lists is just (flip concatMap). Also, this is working with lists, not array

Re: [Haskell-cafe] Is this haskelly enough?

on, which will appear in Data.Function in the next release of base, is defined thusly: on :: (b -> b -> c) -> (a -> b) -> a -> a -> c (*) `on` f = \x y -> f x * f y You can also use Data.Ord.comparing, in this case -- comparing is just (compare `on`). From Ord.hs: -- | -- > comparing p x y

Re: [Haskell-cafe] Getting lambdabot to work with 6.6.1

I also commented out "arrows" as a dependency in the .cabal, I think. Was that not a good idea? it seemed to work. Shachaf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe