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Today's Topics:
1. Re: Fwd: cis194 hw7 question - getting example to work
(Dustin Lee)
2. Re: typeclass woes...how to constain a typeclass to be
"closed" under an operation.... (David McBride)
3. Re: typeclass woes...how to constain a typeclass to be
"closed" under an operation.... (Nicholls, Mark)
----------------------------------------------------------------------
Message: 1
Date: Tue, 6 Jan 2015 09:17:28 -0700
From: Dustin Lee <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Fwd: cis194 hw7 question - getting
example to work
Message-ID:
<CAN3sYc23415KRe=xutd659u0gm-4rkfbdaqcu_7z+1xs4xm...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hmmm... wasn't able to use cabal: (note I use tsocks regularly to get
around our firewall)
sudo tsocks cabal update
Downloading the latest package list from hackage.haskell.org
Warning: http error: Network.Browser.request: Error raised ErrorClosed
cabal: Network.Browser.request: Error raised ErrorClosed
But I was able to install using:
sudo tsocks apt-get install libghc-ghc-mtl-dev
I guess I'll practice using cabal at home...
On Mon, Jan 5, 2015 at 2:30 PM, Christopher Allen <[email protected]> wrote:
> You can see examples of how to use Cabal and sandboxes to install packages
> like mtl in an article I wrote for HowIStart:
>
> http://howistart.org/posts/haskell/1
>
> People are getting steered toward minimal GHC installs on purpose. New
> people have to learn how to install packages anyway. You just have to show
> them and then they can handle it fine.
>
> --- Chris Allen
>
>
> On Mon, Jan 5, 2015 at 3:28 PM, Brandon Allbery <[email protected]>
> wrote:
>
>> On Mon, Jan 5, 2015 at 3:28 PM, Dustin Lee <[email protected]> wrote:
>>
>>> Is my haskell install messed up? Have the libraries changed since the
>>> homework was created?
>>>
>>
>> It sounds like you have a minimal ghc installation. Many things were
>> shifted from ghc's minimal install to the Haskell Platform.
>>
>> --
>> brandon s allbery kf8nh sine nomine
>> associates
>> [email protected]
>> [email protected]
>> unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
--
Dustin Lee
qhfgva=rot13(dustin)
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Message: 2
Date: Tue, 6 Jan 2015 11:41:09 -0500
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] typeclass woes...how to constain a
typeclass to be "closed" under an operation....
Message-ID:
<can+tr40hctlm5fkyyo6yzyr-mqr8eekpcuqcvouapaz7vka...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I think you've slightly surpassed the skill level of this list. You might
try on haskell-cafe, and I would bet you could get an in depth answer on
stackoverflow.
On Tue, Jan 6, 2015 at 3:46 AM, Nicholls, Mark <[email protected]>
wrote:
> I dont seem to have any replies
> Booo
> Is my question too stupid? Or boring? Or unintelligable?
>
> Its quite common in maths to have operations in a theory that are (set)
> closed, i just want to translate that notion to a typeclass
>
> I have a suggestion that does work
>
> Class Foo m where
> op :: m a -> m (S a)
>
> That is closed, but now were working on types of kind ? -> ?, which is
> another leap of complexity
>
> Is this the idiom/pattern i should follow? Or can the closure contraint
> be expressed directly?
>
>
>
> Excuse the spelling, sent from a phone with itty bitty keys, it like
> trying to sow a button on a shirt with a sausage.
>
>
> On 5 Jan 2015, at 10:54, Nicholls, Mark <[email protected]> wrote:
>
> > {-# LANGUAGE TypeFamilies, MultiParamTypeClasses, FlexibleContexts,
> FlexibleInstances, GADTs #-}
>
>
>
> lets say I have a data type
>
>
>
> > data S a = S a deriving Show
>
>
>
> and a nice simple typeclass
>
>
>
> > class Foo a where
>
> > inc :: a -> S a
>
>
>
> make Integer an instance and....
>
>
>
> > instance Foo Integer where
>
> > inc x = S x
>
>
>
> brilliant...
>
>
>
> now lets say I want my typeclass to enforce that any result of inc is also
> of a type that is an instance of the typeclass
>
> I'll follow my nose...which causes me a problem that makes me realise I
> maybe I don't understand whats going on.
>
>
>
> > class Bar a where
>
> > inc' :: (Bar (S a)) => a -> S a
>
>
>
> follow it to....
>
>
>
> > instance Bar Integer where
>
> > inc' x = S x
>
>
>
> this WORKS!...even though "S Integer" is not an instance of Bar!...maybe I
> don't understand.
>
>
>
> > -- x = inc' (1 :: Integer)
>
>
>
> This would go BOOM ....?no instance of (Bar (S Integer))"
>
> ...so that makes sense....
>
>
>
> How do I force Haskell to check the constraint before I evaluate an
> expression?
>
>
>
> follow my nose?
>
>
>
> > -- class (Baz (S a)) => Baz a where
>
> > -- inc'' :: a -> S a
>
>
>
> BOOM ...."Cycle in class declaration"....
>
> booo..but I suppose thats understandable....
>
>
>
> so
>
>
>
> a) is my use of typeclasses correct?...or am I missing something?
>
> b) if so, how do I force the compiler to make sure my typeclass operations
> is nicely closed (under the typeclass)?
>
>
>
>
>
>
>
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Message: 3
Date: Tue, 6 Jan 2015 17:39:57 +0000
From: "Nicholls, Mark" <[email protected]>
To: "The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell" <[email protected]>
Subject: Re: [Haskell-beginners] typeclass woes...how to constain a
typeclass to be "closed" under an operation....
Message-ID:
<e7e7fdf32472ff48bb0e4d9dc4283d0e83853...@mtvne-exmb02.mtvne.ad.viacom.com>
Content-Type: text/plain; charset="iso-8859-1"
I can do the basic Haskell...I've done a course even, but as I don't use it...
I quickly degenerate into a beginner.
I think I've refound my feet....I will post it to the caf? and see what happens.
From: Beginners [mailto:[email protected]] On Behalf Of David
McBride
Sent: 06 January 2015 4:41 PM
To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level
topics related to Haskell
Subject: Re: [Haskell-beginners] typeclass woes...how to constain a typeclass
to be "closed" under an operation....
I think you've slightly surpassed the skill level of this list. You might try
on haskell-cafe, and I would bet you could get an in depth answer on
stackoverflow.
On Tue, Jan 6, 2015 at 3:46 AM, Nicholls, Mark
<[email protected]<mailto:[email protected]>> wrote:
I dont seem to have any replies
Booo
Is my question too stupid? Or boring? Or unintelligable?
Its quite common in maths to have operations in a theory that are (set) closed,
i just want to translate that notion to a typeclass
I have a suggestion that does work
Class Foo m where
op :: m a -> m (S a)
That is closed, but now were working on types of kind * -> *, which is another
leap of complexity
Is this the idiom/pattern i should follow? Or can the closure contraint be
expressed directly?
Excuse the spelling, sent from a phone with itty bitty keys, it like trying to
sow a button on a shirt with a sausage.
On 5 Jan 2015, at 10:54, Nicholls, Mark
<[email protected]<mailto:[email protected]>> wrote:
> {-# LANGUAGE TypeFamilies, MultiParamTypeClasses, FlexibleContexts,
> FlexibleInstances, GADTs #-}
lets say I have a data type
> data S a = S a deriving Show
and a nice simple typeclass
> class Foo a where
> inc :: a -> S a
make Integer an instance and....
> instance Foo Integer where
> inc x = S x
brilliant...
now lets say I want my typeclass to enforce that any result of inc is also of a
type that is an instance of the typeclass
I'll follow my nose...which causes me a problem that makes me realise I maybe I
don't understand whats going on.
> class Bar a where
> inc' :: (Bar (S a)) => a -> S a
follow it to....
> instance Bar Integer where
> inc' x = S x
this WORKS!...even though "S Integer" is not an instance of Bar!...maybe I
don't understand.
> -- x = inc' (1 :: Integer)
This would go BOOM ...."no instance of (Bar (S Integer))"
...so that makes sense....
How do I force Haskell to check the constraint before I evaluate an expression?
follow my nose?
> -- class (Baz (S a)) => Baz a where
> -- inc'' :: a -> S a
BOOM ...."Cycle in class declaration"....
booo..but I suppose thats understandable....
so
a) is my use of typeclasses correct?...or am I missing something?
b) if so, how do I force the compiler to make sure my typeclass operations is
nicely closed (under the typeclass)?
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you communicate with us by e-mail, you acknowledge and assume these risks, and
you agree to take appropriate measures to minimise these risks when e-mailing
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Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be
Viacom, Viacom International Media Networks and VIMN and Comedy Central are all
trading names of MTV Networks Europe. MTV Networks Europe is a partnership
between MTV Networks Europe Inc. and Viacom Networks Europe Inc. Address for
service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.
_______________________________________________
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service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.
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