gmane.comp.lang.haskell.cafe

Re: HTML framework for web-ui

Heinrich Apfelmus — 2013-05-23T14:05:28

Thanks! Only examples and Haddock documentation so far, though the 
latter is extensive.


The current API probably won't change much until the first release, but 
I can't guarantee anything beyond that. It involves lots of aesthetic 
decisions.


That would be one of the corners where it's not ready for public 
consumption yet. ;)


Best regards,
Heinrich Apfelmus

--
http://apfelmus.nfshost.com

Re: ANNOUNCE: new bridge! (prelude-prime)

Roman Cheplyaka — 2013-05-23T13:13:51

* Manuel Gómez <targen< at >gmail.com> [2013-05-23 08:33:15-0430]

No, it definitely isn't.

Roman

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: ANNOUNCE: new bridge! (prelude-prime)

Manuel Gómez — 2013-05-23T13:03:15

Is this strategy adequate for attacking the issue of the type class
stack, though?  Defining, say, a new Monad class with the desired
Functor constraint wouldn’t be of much use, as everything else on
Hackage (and on the GHC libraries!) would still use the “real” Monad.

I still see value in this package — a conservative extension to the
Prelude would certainly come in handy.  Thanks!

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: question about type constructors

Roman Cheplyaka — 2013-05-23T11:54:32

* TP <paratribulations< at >free.fr> [2013-05-23 13:23:36+0200]

No, because the type variables are independent across different
constructors.  They are (implicitly) existentially quantified, which
becomes clearer if you rewrite your type as

  data Person (c :: Gender)
    = forall a b . (PrettyPrint (Person a), PrettyPrint (Person b))
      => Child1 String (Person a) (Person b)
    | forall a b . (PrettyPrint (Person a), PrettyPrint (Person b))
      => Child2 String (Person a) (Person b)
    | ...

What you can do is factor out the Child type as

  data Child where
    Child :: ( PrettyPrint (Person a)
             , PrettyPrint (Person b)
             ) => String -> Person a -> Person b -> Child

  data Person a where
    Child1 :: Child -> Person c
    Child2 :: Child -> Person c
    Child3 :: Child -> Person c

Re: question about type constructors

TP — 2013-05-23T11:23:36


Thanks a lot. Now I am using FlexibleContexts, and it works correctly (see 
code below). I think I have understood the problem.
However, I have still one question. In the code below, I have added data 
constructors "Child2", "Child3" (imagining a world where every people has 
three children). The problem is that I am compelled to repeat the context 
"(PrettyPrint (Person a), PrettyPrint (Person b))" for each one of the 
constructors. Is there any way to specify the context only once? I have 
tried using "forall", but without any success.

Thanks,

TP

-------------
{-# LANGUAGE GADTs #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}

class PrettyPrint a where
    prettify :: a -> String

data Gender = Male | Female | Gender3 | Gender4

data Person :: Gender -> * where
    Person :: String -> Person b
    Child1 :: (PrettyPrint (Person a)
             , PrettyPrint (Person b)
             ) => String -> Person a -> Person b ->

Re: ANNOUNCE: new bridge! (prelude-prime)

Bas van Dijk — 2013-05-23T10:46:05

I see. Thanks for the clarification.

Re: ANNOUNCE: new bridge! (prelude-prime)

Joachim Breitner — 2013-05-23T09:54:32

Hi,

Am Donnerstag, den 23.05.2013, 11:52 +0200 schrieb Bas van Dijk:

manually...

you create a .hs file for every module in base, which imports the module
in base (using a package-qualified import), gives it a qualified name
and puts that name in the export list.

Greetings,
Joachim

Re: ANNOUNCE: new bridge! (prelude-prime)

Bas van Dijk — 2013-05-23T09:52:58

How would you re-export all base's modules from the prelude-prime
package? I didn't know this was already possible.

Bas

Re: ANNOUNCE: new bridge! (prelude-prime)

Michael Snoyman — 2013-05-23T09:36:33

On Thu, May 23, 2013 at 11:38 AM, Anton Kholomiov <anton.kholomiov< at >gmail.com

I'm not necessarily opposed to this idea, but I'd like to point out that it
can have a negative impact on readability of an individual module, since
you can't tell which Prelude is being used. This is the same argument used
for putting LANGUAGE pragmas in a modules instead of listing them in a
cabal file. I think in the case of an alternate Prelude, the argument is
stronger, since language extensions often don't change the meaning of code,
but instead allow previously invalid code to be valid.

Michael
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: ANNOUNCE: new bridge! (prelude-prime)

Joachim Breitner — 2013-05-23T09:26:26

HI,

Am Donnerstag, den 23.05.2013, 12:38 +0400 schrieb Anton Kholomiov:

as far as I know, GHC simply issues an implicit

import Prelude

without package qualifiers. So you can get what you want by not
depending on base, but rather have prelude-prime re-export all modules
from base plus its own Preldue.

A more modular variant would be to have a package "preludeless-base"
which re-exports all modules from base but the prelude. Then you can
select which prelude you want simply by depending on preludeless-base
(instead of base) plus a package (say prelude-prime) which exports a
module named Prelude.

If prelude-prime itself wants to use base, it can still use
package-qualified imports. Or it could itself be based on
preludeless-base.

Greetings,
Joachim

Re: ANNOUNCE: new bridge! (prelude-prime)

Anton Kholomiov — 2013-05-23T08:38:25

I wish it was possible to use an extension

CustomPrelude = Prelude.Prime

In the cabal file




2013/5/23 Roman Cheplyaka <roma< at >ro-che.info>

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

ANNOUNCE: new bridge! (prelude-prime)

Roman Cheplyaka — 2013-05-23T07:37:46

I liked Andreas's idea (cited below). Hence the new package
prelude-prime.

https://github.com/feuerbach/prelude-prime
http://hackage.haskell.org/package/prelude-prime

Pull requests are welcome, but let's stick to widely agreed changes
(like the Foldable/Traversable one). I think one of the reasons why
other Preludes haven't been adopted is because they were too radical.

Let's see whether people here can put their code where their mouth is :)

Roman

* Andreas Abel <andreas.abel< at >ifi.lmu.de> [2013-05-20 13:26:05+0200]

Re: HTML framework for web-ui

Vlatko Basic — 2013-05-23T06:34:49

Hi Heinrich,

Looks simple and interesting. I browsed the git, but not much docs yet.
Just examples, or have I looked at wrong places?


I see that API is still under heavy design. When do you expect the API might 
stabilize?

(BTW, examples in Readme do not work.)

vlatko

Re: How to throw an error if using "cabal-install" < version XYZ?

Carter Schonwald — 2013-05-23T06:21:51

constraining it to >= 1.17 would be better while 1.18 isn't out yet..


On Thu, May 23, 2013 at 1:42 AM, Roman Cheplyaka <roma< at >ro-che.info> wrote:

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: question about type constructors

Roman Cheplyaka — 2013-05-23T06:22:23

* TP <paratribulations< at >free.fr> [2013-05-23 00:34:57+0200]

The rule of thumb is that you should never use IncoherentInstances.

The proper way to do it is:

  data Person :: Gender -> * where
      Person :: String -> Person b
      Child
        :: (PrettyPrint a, PrettyPrint b)
        => String -> Person a -> Person b -> Person c

Roman

Re: How to throw an error if using "cabal-install" < version XYZ?

Carter Schonwald — 2013-05-23T03:53:35

Hey Ryan,
I ran into a related issue, heres a a way you can do this safe IN the cabal
file (or at least you can modify my hack for your purposes)

heres a link to the workaround I did for making LLVM-hs work across >= 1.17
and < 1.17 cabal, but you could abuse it to make sure setup.hs barfs on old
cabal https://github.com/bos/llvm/blob/master/base/Setup.hs#L89-L116

heres a quick one off gist that takes my trick and does something helpful
for you variant + makes sure the tool can't build otherwise

https://gist.github.com/cartazio/5632636

I just wrote a snippet that you can just add to your setup.hs and it should
guarantee the setup.hs will barf with a helpful error message on cabal <
1.17.0


On Wed, May 22, 2013 at 10:50 PM, Ryan Newton <rrnewton< at >gmail.com> wrote:

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

question about type constructors

TP — 2013-05-22T22:34:57

Hi,

In the program I am trying to write, I have a problem that can be reduced to 
the following dummy example:

--------------------------
{-# LANGUAGE GADTs #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE IncoherentInstances #-}

class PrettyPrint a where
    prettify :: a -> String

data Gender = Male | Female | Gender3 | Gender4

data Person :: Gender -> * where
    Person :: String -> Person b
    Child :: String -> Person a -> Person b -> Person c

instance PrettyPrint (Person a)

instance PrettyPrint (Person Male) where
    prettify (Person name) = "My name is " ++ (show name)
          ++ " and I am a male"
    prettify (Child name person1 person2) = "My name is " ++ (show name)
          ++ " and my parents are:" ++ (prettify person1) ++ ", "
          ++ (prettify person2)

main = do

let p1 = Person "Jim" :: Person Male
let p2 = Person "Joe" :: Person Male
let p3 = Child "Jack" p1 p2

print $ prettify p1
print $ prettify p2
print $ pre

Debugging embedded ruby interpreter

Simon Marechal — 2013-05-22T21:36:47

Hello,

I am trying to embed a ruby interpreter into my Haskell library. It
didn't seem complicated, and went flawlessly until I tried using it a
lot. Then I got segfaults.

Here is a test program that corrupts the Array object that is being
created :

https://github.com/bartavelle/hruby/blob/271d99e26a5df075b1011e4b30adf6adddd1c8d2/test/roundtrip.hs

Changing line 46 to this makes it work:

v <- pick (listOf arbitrary :: Gen [Double])

And this version makes it fail again :

v <- pick (listOf subvalue :: Gen [Value])

As you can see, the "frequencies" of "subvalue" are set so that only
JSON Values representing Doubles are generated. As the toRuby and
fromRuby instances for Value are just pure wrappers over the instances
for Double, the non-pure code that is executed should be the same. Am I
wrong here ?

Given that there is almost no documentation for doing this Ruby
embedding, I am unsure that I am doing it right. I looked at the Hubris
code and several other sources on the Internet, but can't find what i

Re: "Haskell from N00b to Real World Programmer"

2013-05-22T19:54:57

Hi - Please record the sessions and post online.

On Wednesday, May 22, 2013 11:45:05 AM UTC-4, Mihai Maruseac wrote:
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: accessing a type variable in instance declaration

Roman Cheplyaka — 2013-05-22T17:40:57

* TP <paratribulations< at >free.fr> [2013-05-22 18:45:06+0200]

You seem to assume that Succ Zero will have type 'Succ 'Zero (i.e. the
promoted type), but it's not the case — it still has type Nat, as
always.

On the other hand, the type 'Succ 'Zero has kind 'Nat and doesn't have
any inhabitants — only types of kind * do.

So, how to fix this depends on what you want. For example, you can
change c2num to accept Proxy c instead of c. Or you can establish the
connection between Succ Zero and 'Succ 'Zero — again, using a (slightly
modified) Sing class. In the latter case, take a look at the
'singletons' package — it can do a lot of work for you.

Roman

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe< at >haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe

Re: accessing a type variable in instance declaration

TP — 2013-05-22T16:45:06


Ok, thanks, I understand. Now, I'm stuck to compile this code (independent 
from my previous post, but related to it):

---------------
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}

data Nat = Zero | Succ Nat
type One = Succ Zero
type Two = Succ One