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Today's Topics:
1. Re: Are tuples really needed? (Carlos J. G. Duarte)
2. Re: associative arrays (Karl Voelker)
3. Re: Are tuples really needed? (Dmitry Vyal)
4. Re: associative arrays (Dmitry Vyal)
5. complex typeclass/constraint question (Dennis Raddle)
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Message: 1
Date: Tue, 28 Aug 2012 23:07:34 +0100
From: "Carlos J. G. Duarte" <carlos.j.g.dua...@gmail.com>
Subject: Re: [Haskell-beginners] Are tuples really needed?
To: beginners@haskell.org
Message-ID: <503d4126....@gmail.com>
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Message: 2
Date: Tue, 28 Aug 2012 23:19:20 -0700
From: Karl Voelker <ktvoel...@gmail.com>
Subject: Re: [Haskell-beginners] associative arrays
To: beginners@haskell.org
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On Sat, Aug 25, 2012 at 8:11 AM, Nick Vanderweit
<nick.vanderw...@gmail.com> wrote:
> I'd still recommend Data.Map, since it's a much more efficient data structure
> for the task.
Data.Map.lookup has better asymptotic time complexity than
Prelude.lookup, but the relevant measures of efficiency depend on the
situation.
-Karl
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Message: 3
Date: Wed, 29 Aug 2012 10:21:16 +0400
From: Dmitry Vyal <akam...@gmail.com>
Subject: Re: [Haskell-beginners] Are tuples really needed?
To: "Carlos J. G. Duarte" <carlos.j.g.dua...@gmail.com>
Cc: beginners@haskell.org
Message-ID: <503db4dc.2070...@gmail.com>
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> Wouldn't Haskell be "cleaner" if it had left tuples out, replacing
them with some standard types added (Pair, Triple, ...) and similar fst,
snd functions? Then curry and uncurry wouldn't even be needed if I have
this right.
I guess it's a matter of syntax. Arguably (x,y) is much clearer and
closer to mathematical notation than Pair x y. Don't forget, the same
story for lists, you can represent [a,b,c] with Cons a (Cons b (Cons c
Nil)) but from ancient times of lispers use a syntactic sugar for that.
------------------------------
Message: 4
Date: Wed, 29 Aug 2012 10:25:41 +0400
From: Dmitry Vyal <akam...@gmail.com>
Subject: Re: [Haskell-beginners] associative arrays
To: Karl Voelker <ktvoel...@gmail.com>, beginners@haskell.org
Message-ID: <503db5e5.2010...@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 29.08.2012 10:19, Karl Voelker wrote:
>
> Data.Map.lookup has better asymptotic time complexity than
> Prelude.lookup, but the relevant measures of efficiency depend on the
> situation.
>
Can you please elaborate a bit? I suspect lists better when there are
just a few elements, but how much is a "few"? And what's about storage
efficiency? How big is (Data.Map.fromList [1])?
------------------------------
Message: 5
Date: Wed, 29 Aug 2012 00:28:37 -0700
From: Dennis Raddle <dennis.rad...@gmail.com>
Subject: [Haskell-beginners] complex typeclass/constraint question
To: Haskell Beginners <beginners@haskell.org>
Message-ID:
<CAKxLvor=FUA0LurCPsoXyMPGAA=hwuxr_g4ejubol70ox_t...@mail.gmail.com>
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{- I'm writing code to do some combinatorial construction via test-and-evaluate
algorithms. And I want to write a very generic algorithm. The idea is
that the item being constructed has a current state, which is
represented by a data type of typeclass EvalState. And the algorithm
will consider a set of new elements to add to the object being
constructed, represented by a data type of typeclass ElemSet. Here are
the class definitions:
-}
class ElemSet a where
elemSetNumElements :: a -> Int
class EvalState s where
isCompleteState :: s -> Bool
newElemSet :: ElemSet a => s -> a
integrateElem :: ElemSet a => a -> Int -> s -> s
-- given an elem set, and an index of the elem to choose , compute a score
scoreElem :: ElemSet a => a -> Int -> s -> EvalScore
type EvalScore = Float
type RandomnessChooser = [(EvalScore,Int)] -> ErrorRand Int
{- here's my generic search algorithm written using the typeclasses
the problem I'm having relates to the fact that I need to call
'integrateElem' which is a function in typeclass EvalState, and one of
the arguments has the constraint of being of typeclass ElemSet, but I
don't know how to put that constraint in.
The specific error is
"Ambigous type variable 'a' in the constraint: 'ElemSet a' arising
from a use of 'integrateElem'"
-}
search :: (EvalState s) =>
RandomnessChooser -> s -> ErrorRand ssearch chooser state = do
if isCompleteState state
then return state
else do
let elemSet = newElemSet state
n = elemSetNumElements elemSet
scores = map g [0..n-1]
g i = (scoreElem elemSet i state,i)
chosenElemIdx <- chooser scores
let newState = integrateElem elemSet chosenElemIdx state
search chooser newState
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