Hello again,
I think that I have done all of the above in different situations, and
so I don't think that there is a single correct answer. I usually
avoid using the newtype trick as I find it inconvenient: usually
the newtype does not have the same operations as the underlying type
and so
Hi folks
I have been known to venture the viewpoint that the
newtype trick might benefit from improved library
support, for example, here
http://www.mail-archive.com/haskell-cafe@haskell.org/msg37213.html
This is in a similar vein to Derek's approach, if
accompanied by a little more
Hello,
I don't mean to be negative here but I really fail to see how do any
of these ideas help the situation. (I do think it would be cool to
have a generic way to lift functions from one type to another that is
isomorphic to it). The fundamental problem is that there are multiple
functions of
Luke Palmer wrote:
On Mon, Jan 19, 2009 at 3:58 AM, Patai Gergely patai_gerg...@fastmail.fmwrote:
However, there are other type classes that are too general to assign
such concrete uses to. For instance, if a data structure can have more
than one meaningful (and useful) Functor or Monoid
Patai Gergely wrote:
Hi everyone,
I have a general program design question, but I can't really think of
good examples so it will be a bit vague. There was a discussion on Show
not long ago which brought up the problem that there are several ways to
show a data structure, and it depends on the
As for multiple Monoid or Functor instances, simply define a newtype,
as it is done in Data.Monoid.
What part of your question does that answer and what part doesn't it?
2009/1/19 Patai Gergely patai_gerg...@fastmail.fm:
Hi everyone,
I have a general program design question, but I can't really
On Mon, Jan 19, 2009 at 3:58 AM, Patai Gergely patai_gerg...@fastmail.fmwrote:
However, there are other type classes that are too general to assign
such concrete uses to. For instance, if a data structure can have more
than one meaningful (and useful) Functor or Monoid instance,
As a side
2009/1/19 Luke Palmer lrpal...@gmail.com:
As a side curiosity, I would love to see an example of any data structure
which has more than one Functor instance. Especially those which have more
than one useful functor instance.
(,) ?
-Antoine
___
2009/1/19 Luke Palmer lrpal...@gmail.com:
On Mon, Jan 19, 2009 at 3:58 AM, Patai Gergely patai_gerg...@fastmail.fm
wrote:
However, there are other type classes that are too general to assign
such concrete uses to. For instance, if a data structure can have more
than one meaningful (and
Am Montag, 19. Januar 2009 14:31 schrieb Antoine Latter:
2009/1/19 Luke Palmer lrpal...@gmail.com:
As a side curiosity, I would love to see an example of any data structure
which has more than one Functor instance. Especially those which have
more than one useful functor instance.
(,) ?
Am Montag, den 19.01.2009, 14:47 +0100 schrieb Daniel Fischer:
Am Montag, 19. Januar 2009 14:31 schrieb Antoine Latter:
2009/1/19 Luke Palmer lrpal...@gmail.com:
As a side curiosity, I would love to see an example of any data structure
which has more than one Functor instance. Especially
The desugaring of (, a) would involve some type level lambda, and
that's not something that is available (yet).
-- Lennart
On Mon, Jan 19, 2009 at 1:49 PM, Holger Siegel holgersiege...@yahoo.de wrote:
Am Montag, den 19.01.2009, 14:47 +0100 schrieb Daniel Fischer:
Am Montag, 19. Januar 2009
As a side curiosity, I would love to see an example of any data structure
which has more than one Functor instance. Especially those which have
more than one useful functor instance.
data Record a b = R { field1 :: a, field2 :: b }
If I want to use fmap to transform either field, I have to
Hello,
The multitude of newtypes in the Monoid module are a good indication
that the Monoid class is not a good fit for the class system (it is
ironic that discussing it resulted in such a huge thread recently :-).
How I'd approach the situation that you describe would depend on
the context
On Mon, 2009-01-19 at 10:59 -0800, Iavor Diatchki wrote:
Hello,
The multitude of newtypes in the Monoid module are a good indication
that the Monoid class is not a good fit for the class system
I would say rather that the class system is not a good fit for Monoid.
Proposals for local
Hi,
On Mon, Jan 19, 2009 at 11:06 AM, Jonathan Cast
jonathancc...@fastmail.fm wrote:
On Mon, 2009-01-19 at 10:59 -0800, Iavor Diatchki wrote:
Hello,
The multitude of newtypes in the Monoid module are a good indication
that the Monoid class is not a good fit for the class system
I would say
This is one of the shortcomings of haskell not to mention other programming
languages. Mathemathicist would find it very annoying.
Instead of
instance Monoid Integer where
mappend = (+)
mempty = 0
instance Monoid Integer where
mappend = (*)
mempty = 1
which is not legal and the
On Mon, 2009-01-19 at 12:10 -0800, Iavor Diatchki wrote:
I usually
avoid using the newtype trick as I find it inconvenient: usually
the newtype does not have the same operations as the underlying type
and so it cannot be used directly, and if you are going to wrap thing
just when you
On Mon, 2009-01-19 at 21:18 +0100, Alberto G. Corona wrote:
This is one of the shortcomings of haskell not to mention other
programming languages. Mathemathicist would find it very annoying.
Instead of
instance Monoid Integer where
mappend = (+)
mempty = 0
instance Monoid
I'd prefer something like
Sum :: Monoid Integer
Sum = Monoid {mappend = (+), mempty = 0}
Prod :: Monoid Integer
Prod = Monoid {mappend = (*), mempty = 1}
instance Sum in [some code using mempty and mappend]
On 19 Jan 2009, at 23:18, Alberto G. Corona wrote:
This is one of the shortcomings of
On Mon, 2009-01-19 at 12:10 -0800, Iavor Diatchki wrote:
Hi,
On Mon, Jan 19, 2009 at 11:06 AM, Jonathan Cast
jonathancc...@fastmail.fm wrote:
On Mon, 2009-01-19 at 10:59 -0800, Iavor Diatchki wrote:
Hello,
The multitude of newtypes in the Monoid module are a good indication
that the
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