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RE: Arrow Classes
by Simon Peyton-Jones 30 Jun '03

30 Jun '03

It may interest you guys to know that Ross Paterson and I have just put syntactic support for arrows into GHC. It's only in the CVS version at the moment, and is not documented at all, but those things will come. The type error messages should, I hope, be a lot better than those one can get by type checking pre-processed code. Simon | -----Original Message----- | From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Joe | English | Sent: 28 June 2003 17:01 | To: haskell-cafe(a)haskell.org | Subject: Re: Arrow Classes | | | Ashley Yakeley wrote: | > Wolfgang Jeltsch wrote: | > | > > This brings me to another point. One year ago we had a discussion on The | > > Haskell Mailing List concerning arrows. (The subject of the mails was just | > > "arrows".) The point was that it seemed strange to me that first and second | > > are included in the basic arrow class Arrow while left and right have their | > > extra class ArrowChoice. Not only that it seemed strange to me but it made | > > impossible to make Parser baseMonad an instance of Arrow. Parser baseMonad | > > has nice implementations of pure and (>>>) but none of first or second. | > | > I agree. My own Arrow module hierarchy looks more or less like this: | > | > class Compositor comp where [...] | > class (Compositor arrow) => Arrow arrow where [...] | > class (Arrow arrow) => ProductArrow arrow where [...] | > class (Arrow arrow) => CoproductArrow arrow where [...] | > class (ProductArrow arrow,CoproductArrow arrow) => FullArrow arrow | > instance (ProductArrow arrow,CoproductArrow arrow) => FullArrow arrow | > class (Arrow arrow) => ArrowFix arrow where [...] | > class (FullArrow arrow) => ApplyArrow arrow where [...] | | | On that topic, see below for what mine looks like | (from HXML, <URL: http://www.flightlab.com/~joe/hxml/ >). | | I started off with Hughes' conventions, but for some | reason could never remember the difference between &&& and ***, | or between ||| and +++. I found &&&, >&<, |||, >|< to have | better mnemonic value. This also frees up +++ for ArrowPlus, | which -- in HXML applications -- is frequently used and should | thus be easy to type. | | When using the ArrowChoice operators, I kept tripping over all | the 'Either' coproduct types, so added some syntactic sugar | (borrowed from HaXML): | | data Choice a = a :> a | class (Arrow a) => ArrowChoice a where | [ ... ] | ( ?>) :: (b -> Bool) -> Choice (a b c) -> a b c | (>?>) :: a b Bool -> Choice (a b c) -> a b c | | I found "p ?> f :> g" much more pleasant to use. | | (I also like the idea of splitting the product operators out of | the base Arrow class -- will consider doing that in my library). | | -- | | infixr 5 +++ | infixr 3 >&<, &&& | infixr 2 >|<, |||, ?>, >?>, :> | infixl 1 >>> | | class Arrow a where | arr :: (b -> c) -> a b c | (>>>) :: a b c -> a c d -> a b d | apfst :: a b c -> a (b,x) (c,x) | apsnd :: a b c -> a (x,b) (x,c) | (>&<) :: a b c -> a d e -> a (b,d) (c,e) | (&&&) :: a b c -> a b d -> a b (c,d) | liftA2 :: (b -> c -> d) -> a e b -> a e c -> a e d | aConst :: c -> a b c | idArrow :: a b b | -- Minimal implementation: arr, >>>, apfst or >&< | | data Choice a = a :> a | class (Arrow a) => ArrowChoice a where | apl :: a b c -> a (Either b d) (Either c d) | apr :: a b c -> a (Either d b) (Either d c) | (>|<) :: a b c -> a d e -> a (Either b d) (Either c e) | (|||) :: a b c -> a d c -> a (Either b d) c | ( ?>) :: (b -> Bool) -> Choice (a b c) -> a b c | (>?>) :: a b Bool -> Choice (a b c) -> a b c | -- Minimal implementation: >|< or apl | | class (Arrow a) => ArrowApply a where | app :: a (a b c,b) c | | class (Arrow a) => ArrowZero a where | aZero :: a b c | aMaybe :: a (Maybe c) c | aGuard :: (b -> Bool) -> a b b | | class (Arrow a) => ArrowPlus a where | (+++) :: a b c -> a b c -> a b c | | | | --Joe English | | jenglish(a)flightlab.com | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: UML diagrams of Haskell
by Hal Daume 30 Jun '03

30 Jun '03

There's something like UML, called FAD (Functional Analysis and Design, I believe). It was the topic of Daniel Russell's PhD thesis. See http://www.cs.kent.ac.uk/pubs/2001/1152/index.html for more. -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume > -----Original Message----- > From: haskell-cafe-admin(a)haskell.org > [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Bas van Dijk > Sent: Sunday, June 29, 2003 2:50 PM > To: HaskellCafe Mailinglist > Subject: UML diagrams of Haskell > > > Hi, > > It's maybe a weird question but do there exist UML diagrams > of the Haskell > language. > They don't necessarily have to be UML diagrams, as long as > they show the > different concepts in the language (i.e.: functions, > datatypes, patterns, > etc.) and the relations between them(i.e.: a function > consists of other > functions, functions have a type). > > Bas. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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RE: Simple monads
by Hal Daume 29 Jun '03

29 Jun '03

> (a) People could point out to me where I'm still confused, as > revealed by > my code. Is it needlessly complicated? looks pretty reasonable to me :) as to why Unique is in the IO monad is probabyl because if it were in any other monad, you could start the monad twice and thus get a repeat of each ID (if that makes sense). The only way around this is to put it in IO.

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Bom dia haskell-cafe
by Marta 29 Jun '03

29 Jun '03

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Template Haskell question
by Ashley Yakeley 27 Jun '03

27 Jun '03

Can anyone tell me what's wrong with this? -- ghc -fglasgow-exts -c TH.hs module TH where { import Language.Haskell.THSyntax; class HasZero a where { zero :: a; }; aninstance :: TypQ -> Q [Dec]; aninstance t = [d| instance HasZero $t where -- error here { zero = 0; }; |]; $(aninstance [t|Int|]) $(aninstance [t|Integer|]) } $ ghc -fglasgow-exts -c TH.hs TH.hs:14: Malformed context in instance header All I want to do is spin off a number instances for a number of types... -- Ashley Yakeley, Seattle WA

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RE: haskell array access
by Hal Daume 27 Jun '03

27 Jun '03

> At best case for Haskell, 15.5 times slower. The thing about > bounds checking, > in Haskell it's always there. In C, you might have it, you > might not there is > no certainty by the language, only by design and > implementation. So with C, > one is free to live dangerously. If you're using GHC, there's Data.Array.Base.unsafeAt which is the one which doesn't do bounds checking.

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RE: Help with ghci and Yet Another Haskell Tutorial
by Hal Daume 27 Jun '03

27 Jun '03

toUpper is in the Char (or Data.Char) library. You can do: Prelude> :m Data.Char Data.Char> map toUpper "hello world" or specify it completely. Prelude> map Data.Char.toUpper "hello world" I'll fix this reference in YAHT. I believe that Hugs automatically exports toUpper, which is why it was in there to begin with. - Hal -- Hal Daume III | hdaume(a)isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume -----Original Message----- From: haskell-cafe-admin(a)haskell.org [mailto:haskell-cafe-admin@haskell.org] On Behalf Of Mark Espinoza Sent: Friday, June 27, 2003 7:53 AM To: haskell-cafe(a)haskell.org Subject: Help with ghci and Yet Another Haskell Tutorial Greetings, I am going through the Tutorial using ghc on a redhat 8.0 system. Everything works fine untill I get to the map function: Prelude> map toUpper "hello world" <interactive>:1: Variable not in scope: `toUpper' Prelude> Can anyone tel me what is or might be going on? Thanks. Sincerely, Mark Get your free e-mail address at http://felinemail.zzn.com ___________________________________________________________ Get your own Web-based E-mail Service at http://www.zzn.com _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Help with ghci and Yet Another Haskell Tutorial
by Mark Espinoza 27 Jun '03

27 Jun '03

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by Edwin Jones 27 Jun '03

27 Jun '03

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RE: haskell array access
by Simon Peyton-Jones 27 Jun '03

27 Jun '03

Several comments 1. In Haskell "mod" is a lot more expensive than "rem", because it involves careful jiggery pokery with the sign of the result. That's why your boxed version was slower (nothing to do with boxing). 2. GHC does indeed optimise away the array access if you aren't careful, and does in Derek's code. Below is a version that avoids doing so, in the same way as the C version, by returning one of the values. 3. Derek correctly points out that gcc does not do array-bound checks. GHC should eliminate them, but it's a non-trivial analysis and GHC does not currently attempt it. You can always use unsafeAt, as Derek does. 4. The UArray stuff builds an array of unboxed Ints, like C. If you use ordinary boxed arrays, the loop has to unbox the Int every time around the loop, which makes it slower (2.6s) With that done, we get ghc -O2 -fliberate-case-threshold20 1.8s gcc -O2 1.4s Seems close enough to me; have not investigated further. The "liberate-case" thing is a practically-undocumented GHC optimisation that switches on with -O2. It specialises a loop that unboxes a free variable (here the array k) so that the unboxing doesn't happen each time round the loop. The threshold at which GHC thinks there is too much code dup is set very low by default, so the flag increases it. Simon ====================== k :: UArray Int Int k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] acc :: Int -> Int -> Int acc r 0 = r acc r n = r `seq` acc (k `unsafeAt` (n `rem` 16)) (n - 1) main :: IO () main = print (acc 0 100000000) ====================== | Anyways, | int main(void){ | int i, k; | int a [16]; | for (i=0; i<=100000000; i++) { | k = a [i % 16]; | } | printf("%d\n",k); | return 0; | } | compiled with MinGW 3.2 -O/-O2/-O3 runs in 1.8s using time. | | int main(void){ | int i, k; | int a [16]; | for (i=0; i<=100000000; i++) { | k = a [i % 16]; | } | printf("%d\n",k); | return 0; | } | | The following (compiled with -O2 -fglasgow-exts and GHC 6.1 i.e. a CVS | version) beats the C version taking only .8s. They don't do the same | thing (the Haskell version "does" more, but prints something different). | Looking at the core/stg/c/asm (the asm and C was quite messy compared | with other times), it certainly doesn't appear to be optimizing this to | print 0, and it does appear (though I'm less sure here) to be doing | everything as it should, but it's really hard to read the assembly, | since we don't use the value we lookup I can easily see gcc dropping it | altogether, though the C GHC spits out is pretty unusual for gcc, so it | may not. | | module Main (main) where | import Data.Array.Unboxed (UArray, array) | import Data.Array.Base (unsafeAt) -- if C doesn't, why should we? | import GHC.Exts | | k :: UArray Int Int | k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] | | acc :: Int# -> Int# | acc 0# = 0# | acc n = (k `unsafeAt` (I# (n `remInt#` 16#))) `seq` acc (n -# 1#) | | main :: IO () | main = print (I# (acc 100000000#)) | | However, I'm am somewhat surprised that I seemingly had to unbox by hand | to get quite close (in fact, better) than C. I expected the following | version to be comparable to the C version (and it is orders of magnitude | faster than the original version which was over 5min when I killed it | (though I think I compiled it with just -O), this version taking 14s). | | module Main (main) where | import Data.Array.Unboxed (UArray, array) | import Data.Array.Base (unsafeAt) -- if C doesn't, why should we? | | k :: UArray Int Int | k = array (0,15) [(i, i+1) | i <- [0 .. 15] ] | | acc :: Int -> Int | acc 0 = 0 | acc n = (k `unsafeAt` (n `mod` 16)) `seq` acc (n - 1) | | main :: IO () | main = print (acc 100000000) | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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