Send Beginners mailing list submissions to
[email protected]
To subscribe or unsubscribe via the World Wide Web, visit
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
or, via email, send a message with subject or body 'help' to
[email protected]
You can reach the person managing the list at
[email protected]
When replying, please edit your Subject line so it is more specific
than "Re: Contents of Beginners digest..."
Today's Topics:
1. Tree-like Structure with unique elements on each level (martin)
2. Re: Tree-like Structure with unique elements on each level
(Imants Cekusins)
3. Implementing instance of '^' operator ([email protected])
----------------------------------------------------------------------
Message: 1
Date: Sat, 2 Jan 2016 20:53:24 +0100
From: martin <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Tree-like Structure with unique elements
on each level
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello all,
I recently modeled a tree like this:
data Predicate a = Any | Pred (S.Set a)
data Product a = Pany | Prod (S.Set(Predicate a, S.Set(Product a)))
What I wanted to achieve was to have each element only once on each level.
Hence the Sets. But this structure does not
achieve this. I can easily duplicate elements on a level as long as their
subordinates are different, so I might as well
give up working with sets.
Is there a way to construct a tree where each element can occur only once on
each level?
------------------------------
Message: 2
Date: Sat, 2 Jan 2016 22:12:57 +0100
From: Imants Cekusins <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Tree-like Structure with unique
elements on each level
Message-ID:
<CAP1qinagm=rsfzhr9w1v37b_m6utukqt2jjk52lyjoymhcj...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
> data Predicate a = Any | Pred (S.Set a)
data Product a = Pany | Prod (S.Set(Predicate a, S.Set(Product a)))
Does this fit:
data Predicate a = Any | Pred a
data Product a = Pred' (Predicate a) | Prod (Product a)
?
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20160102/e0c65895/attachment-0001.html>
------------------------------
Message: 3
Date: Sat, 2 Jan 2016 22:55:41 -0800
From: <[email protected]>
To: "[email protected]" <[email protected]>
Subject: [Haskell-beginners] Implementing instance of '^' operator
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
As a ?hello world? example for type definitions, I like to define a numeric
type that can handle the mod p multiplicative group, where p is prime. This
requires:
? Implementing interface functions
? Defining non-trivial implementations, where constructor must be private, etc.
? Invoking an abstract superclass concrete instance method from within the
subclass method definition
The latter appears not to be possible in Haskell. Is this true?
Here?s the basic code, but I punted on x^n. It looks like I?d have to paste in
the entire original definition of ?^?.
data Modp a = Modp a a deriving (Eq, Show)
mkModp p n | isPrime p = Modp p (n `mod` p)
| otherwise = error $ show p ++ " is not a prime"
instance Integral a => Num (Modp a) where
(Modp q n) + (Modp p m) | p==q = Modp p $ (n+m) `mod` p
| otherwise = error $ "unequal moduli"
(Modp p n) * (Modp q m) | p==q = Modp p $ (n*m) `mod` p
| otherwise = error $ "unequal moduli"
negate (Modp p n) = Modp p (p-n)
-- can't reuse base because ^ is impl. directly in prelude
{- (Modp p x) ^ n | n <= p = (Modp p x) `baseExp` n
| n1 == 0 = (Modp p x)
| n > p = x ^ n1
where baseExp = ^ in Num
n1 = n `mod` p
-}
instance Integral a => Fractional (Modp a) where
recip (Modp p n) = (Modp p n)^(p-2)
isPrime p = True -- stub
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.haskell.org/pipermail/beginners/attachments/20160102/dd8c3229/attachment-0001.html>
------------------------------
Subject: Digest Footer
_______________________________________________
Beginners mailing list
[email protected]
http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
End of Beginners Digest, Vol 91, Issue 3
****************************************
