Arrow without `>>>'
Valery V. Vorotyntsev
valery.vv at gmail.com
Wed Jan 23 12:20:19 EST 2008
Hi, friends,
I've built GHC from darcs, and...
Could anybody tell me, what's the purpose of Arrow[1] not having `>>>'
method?
1. http://darcs.haskell.org/packages/base/Control/Arrow.hs
$ ghci
GHCi, version 6.9.20080104: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
Prelude> :m + Control.Arrow
Prelude Control.Arrow> :i Arrow
class (Control.Category.Category a) => Arrow a where
arr :: (b -> c) -> a b c
pure :: (b -> c) -> a b c
first :: a b c -> a (b, d) (c, d)
second :: a b c -> a (d, b) (d, c)
(***) :: a b c -> a b' c' -> a (b, b') (c, c')
(&&&) :: a b c -> a b c' -> a b (c, c')
-- Defined in Control.Arrow
instance Arrow (->) -- Defined in Control.Arrow
instance (Monad m) => Arrow (Kleisli m) -- Defined in Control.Arrow
Prelude Control.Arrow> Leaving GHCi.
I can't build[2] arrows-0.3 package without `>>>' in Arrow.
2.
vvv at fun:~/src/arrows$ darcs w
{
hunk ./Control/Arrow/Operations.hs 36
+import Control.Category ((>>>))
hunk ./Control/Arrow/Transformer/CoState.hs 23
+import Control.Category ((>>>))
}
vvv at fun:~/src/arrows$ runhaskell Setup build
Preprocessing library arrows-0.3...
Building arrows-0.3...
[ 3 of 12] Compiling Control.Arrow.Transformer.CoState (
Control/Arrow/Transformer/CoState.hs,
dist/build/Control/Arrow/Transformer/CoState.o )
Control/Arrow/Transformer/CoState.hs:29:7:
`>>>' is not a (visible) method of class `Arrow'
The question arises "should I?", but this is one of lambdabot's[3]
depencies.
3. http://code.haskell.org/lambdabot/
Thanks a lot!
--
vvv
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