On 08/03/12 16:19, Christopher Done wrote:
‘Ello.
Is there a generalization of this operator? It's all over the place,
it's basically
(!) :: (Monad m, Indexed collection index value) = index -
container - m value
We have `(!!)` on lists, `(!)` on maps, vectors, json objects, …
(doesn't
Ops sorry, I had misunderstood, you don't want key-lookups but a simple
indexing. In that case you might want an almost identical class but with
different instances (e.g IxClass [a] Int a, etc.).
Also, I don't see why you need to throw monads in.
Francesco.
Ok, this should suit your needs better, without functional dependencies
as a bonus:
{-# LANGUAGE TypeFamilies, ScopedTypeVariables, FlexibleInstances #-}
module IxClass (IxClass(..)) where
import Data.Map (Map)
import qualified Data.Map as Map
import Data.Hashable (Hashable)
import
On Thu, Mar 8, 2012 at 11:19 AM, Christopher Done
chrisd...@googlemail.com wrote:
‘Ello.
Is there a generalization of this operator? It's all over the place,
it's basically
(!) :: (Monad m, Indexed collection index value) = index -
container - m value
We have `(!!)` on lists, `(!)` on
(Though I seem to recall the monadic return value being frowned upon
but I don't recall why.)
The type signature that you wrote is very generic and doesn't help in
introducing effects while retrieving the indexed value, which I imagine
is what you wanted to do.
I guess you could define a
On 8 March 2012 18:32, Anthony Cowley acow...@seas.upenn.edu wrote:
Perhaps Data.Key meets your needs?
http://hackage.haskell.org/packages/archive/keys/2.1.2/doc/html/Data-Key.html
Ah, perhaps indeed. Thanks!
On 8 March 2012 19:12, Francesco Mazzoli f...@mazzo.li wrote:
The type signature
Because Maybe is already a monad and it's nice to fail in the monad of
choice, e.g. if I'm in the list monad I get empty list instead, or if
I'm in the Result monad from JSON it'll fail in there. ‘Course fail
is suboptimal and MonadError might be better.
'fail' really shouldn't be in Monad. My
On Thu, Mar 08, 2012 at 07:53:48PM +0100, Christopher Done wrote:
On 8 March 2012 18:32, Anthony Cowley acow...@seas.upenn.edu wrote:
Perhaps Data.Key meets your needs?
http://hackage.haskell.org/packages/archive/keys/2.1.2/doc/html/Data-Key.html
Ah, perhaps indeed. Thanks!
On 8 March
On 8 March 2012 21:43, Brent Yorgey byor...@seas.upenn.edu wrote:
‘Course fail is suboptimal and MonadError might be better.
Monads have nothing to do with failure. Instead of Monad you would
want to use something like MonadZero or MonadError.
Yeah that's what I said. GOSH.
On 2/4/07, Eric Olander [EMAIL PROTECTED] wrote:
Hi,
I'm still somewhat new to Haskell, so I'm wondering if there are better
ways I could implement the following functions, especially shiftl:
moves the last element to the head of the list
shiftl :: [a] - [a]
shiftl [] = []
That's a clever routine. It should be faster than mine since it only makes
a single pass though the list. Thanks for all the suggestions from everyone
that responded. Here is a link to some more info on the project I'm working
on if anyone is interested: http://ehaskell.blogspot.com/
-Eric
Not much better. You could define shiftl such that is does a single
traversal and
returns both the last element and all but the last. That will save
you one traversal.
On Feb 4, 2007, at 18:44 , Eric Olander wrote:
Hi,
I'm still somewhat new to Haskell, so I'm wondering if there are
Nicolas Frisby wrote:
I've always thought that when certain operations are of particular
interest, it's time to use more appropriate data structures, right?
Lists are great and simple and intuitive, but if you need such
operations as shifts, something like a deque is the way to go.
This sounds
I agree. If performance is important enough to worry about is shiftl
traverses the list once or twice then it's time to switch to a better
data type.
On Feb 4, 2007, at 19:27 , Yitzchak Gale wrote:
Nicolas Frisby wrote:
I've always thought that when certain operations are of particular
Eric Olander wrote:
Hi,
I'm still somewhat new to Haskell, so I'm wondering if there are
better ways I could implement the following functions, especially shiftl:
moves the first element to the end of the list
shiftr :: [a] - [a]
shiftr [] = []
shiftr (x:y) = y ++ [x]
On Sunday 04 February 2007 14:24, Nicolas Frisby wrote:
I've always thought that when certain operations are of particular
interest, it's time to use more appropriate data structures, right?
Lists are great and simple and intuitive, but if you need such
operations as shifts, something like a
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