Number[A] trait?

Hello,

In Haskell one can define a simple function like this:

Prelude> let add1 x = x + 1
Prelude> add1 2
3
Prelude> add1 2.0
3.0
Prelude> :type add1
add1 :: (Num a) => a -> a

Would it be possible to do the same thing in Scala? I mean:
def add1[U <% Number[U]](x:U) = x + 1

I made several attempt to define a trait Number[A] like in Ordered[A] but all of them failed. I guess if it was easy it would already be there...

Thanks,
Sebastien

Sebastien Bocq wrote:
> a trait Number[A] like in Ordered[A]

http://lampsvn.epfl.ch/svn-repos/scala/scala/branches/devel-base-2.8.0/s...

The code appears in the recent scala-2.8.0... nightly builds from
http://www.scala-lang.org/node/212 : download and install, then expand
src/scala-library-src.jar and see scalax/Numeric.scala

Sebastien Bocq wrote:

a trait Number[A] like in Ordered[A]

http://lampsvn.epfl.ch/svn-repos/scala/scala/branches/devel-base-2.8.0/src/library/scalax/Numeric.scala

The code appears in the recent scala-2.8.0... nightly builds from http://www.scala-lang.org/node/212 : download and install, then expand src/scala-library-src.jar and see scalax/Numeric.scala

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi Luc,
I prefer the flexibility of such a trait:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/Equal....

Then I use === (that's 3 =) and /= methods for comparing for equality:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/EqualW...

Luc Duponcheel wrote:
> Along the same lines:
>
> We all know that equality is a tricky issue
> (cfr. discussion in one of the chapters of the Scala Book)
>
> ... just out of interest ...
>
> I guess that defining equality in terms of a trait Equal[A]
> has never been an option because of Java compatibility issues?
>
> Or am I plain wrong here?
>
> Luc
>
> On Fri, Jan 9, 2009 at 10:37 AM, Eric Willigers
> > wrote:
>
> Sebastien Bocq wrote:
>
> a trait Number[A] like in Ordered[A]
>
>
>
http://lampsvn.epfl.ch/svn-repos/scala/scala/branches/devel-base-2.8.0/s...
>
> The code appears in the recent scala-2.8.0... nightly builds
> from http://www.scala-lang.org/node/212 : download and install,
> then expand src/scala-library-src.jar and see scalax/Numeric.scala
>
>
>
>
> --
> __~O
> -\ <,
> (*)/ (*)
>
> reality goes far beyond imagination
>

- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAklnM3kACgkQmnpgrYe6r63n1ACfdhZexlxixwk6Appfx9RKWSPx
Tj4AoMWLbhjYebFFvUQl5IScFNUpAsSj
=8dqs
-----END PGP SIGNATURE-----

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi Luc,
I prefer the flexibility of such a trait:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/Equal.html

Then I use === (that's 3 =) and /= methods for comparing  for equality:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/EqualW.html


Luc Duponcheel wrote:
> Along the same lines:
>
> We all know that equality is a tricky issue
> (cfr. discussion in one of the chapters of the Scala Book)
>
> ... just out of interest ...
>
> I guess that defining equality in terms of a trait Equal[A]
> has never been an option because of Java compatibility issues?
>
> Or am I plain wrong here?
>
> Luc
>
> On Fri, Jan 9, 2009 at 10:37 AM, Eric Willigers
> <ewilligers@gmail.com <mailto:ewilligers@gmail.com>> wrote:
>
>     Sebastien Bocq wrote:
>
>         a trait Number[A] like in Ordered[A]
>
>
>
http://lampsvn.epfl.ch/svn-repos/scala/scala/branches/devel-base-2.8.0/src/library/scalax/Numeric.scala
>
>     The code appears in the recent scala-2.8.0... nightly builds
>     from http://www.scala-lang.org/node/212 : download and install,
>     then expand src/scala-library-src.jar and see scalax/Numeric.scala
>
>
>
>
> --
>   __~O
>  -\ <,
> (*)/ (*)
>
> reality goes far beyond imagination
>

- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAklnM3kACgkQmnpgrYe6r63n1ACfdhZexlxixwk6Appfx9RKWSPx
Tj4AoMWLbhjYebFFvUQl5IScFNUpAsSj
=8dqs
-----END PGP SIGNATURE-----

Just add some prototypes and get rid of static typing, and I'll be in heaven... or javascript whichever is closer.

On Fri, Jan 9, 2009 at 6:22 AM, Tony Morris <tmorris@tmorris.net> wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi Luc,
I prefer the flexibility of such a trait:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/Equal.html

Then I use === (that's 3 =) and /= methods for comparing  for equality:
http://scalaz.googlecode.com/svn/artifacts/latest/scaladoc/scalaz/EqualW.html


Luc Duponcheel wrote:
> Along the same lines:
>
> We all know that equality is a tricky issue
> (cfr. discussion in one of the chapters of the Scala Book)
>
> ... just out of interest ...
>
> I guess that defining equality in terms of a trait Equal[A]
> has never been an option because of Java compatibility issues?
>
> Or am I plain wrong here?
>
> Luc
>
> On Fri, Jan 9, 2009 at 10:37 AM, Eric Willigers
> <ewilligers@gmail.com <mailto:ewilligers@gmail.com>> wrote:
>
>     Sebastien Bocq wrote:
>
>         a trait Number[A] like in Ordered[A]
>
>
>
http://lampsvn.epfl.ch/svn-repos/scala/scala/branches/devel-base-2.8.0/src/library/scalax/Numeric.scala
>
>     The code appears in the recent scala-2.8.0... nightly builds
>     from http://www.scala-lang.org/node/212 : download and install,
>     then expand src/scala-library-src.jar and see scalax/Numeric.scala
>
>
>
>
> --
>   __~O
>  -\ <,
> (*)/ (*)
>
> reality goes far beyond imagination
>

- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAklnM3kACgkQmnpgrYe6r63n1ACfdhZexlxixwk6Appfx9RKWSPx
Tj4AoMWLbhjYebFFvUQl5IScFNUpAsSj
=8dqs
-----END PGP SIGNATURE-----

On Thu, Jan 08, 2009 at 11:53:48PM +0000, Ricky Clarkson said
> I blogged about something related to this recently, and while my blog
> doesn't answer your question, James Iry provided this code in a comment that
> does:
>
> http://paste.pocoo.org/show/97661/
>
> And a bit of context:
> http://rickyclarkson.blogspot.com/2009/01/typeclass-pattern.html
>

This still does not allow you to write generic sections. I'm not
entirely sure but I think this is because in haskell numeric constants
are polymorphic:

Prelude> :t 1
1 :: (Num t) => t

while in scala they are monomorphic:

scala> 1
res0: Int = 1

This means in haskell the operation will drive the type of the constant
but in scala the constant will drive the type of the operation.

On Thu, Jan 08, 2009 at 11:53:48PM +0000, Ricky Clarkson <ricky.clarkson@gmail.com> said
> I blogged about something related to this recently, and while my blog
> doesn't answer your question, James Iry provided this code in a comment that
> does:
>
> http://paste.pocoo.org/show/97661/
>
> And a bit of context:
> http://rickyclarkson.blogspot.com/2009/01/typeclass-pattern.html
>

This still does not allow you to write generic sections. I'm not
entirely sure but I think this is because in haskell numeric constants
are polymorphic:

 Prelude> :t 1
 1 :: (Num t) => t

while in scala they are monomorphic:

 scala> 1
 res0: Int = 1

This means in haskell the operation will drive the type of the constant
but in scala the constant will drive the type of the operation.

The technique in my blog post allows generic sections, whereas James' code snippet doesn't.

2009/1/9 Geoff Reedy <geoff@programmer-monk.net>

On Thu, Jan 08, 2009 at 11:53:48PM +0000, Ricky Clarkson <ricky.clarkson@gmail.com> said
> I blogged about something related to this recently, and while my blog
> doesn't answer your question, James Iry provided this code in a comment that
> does:
>
> http://paste.pocoo.org/show/97661/
>
> And a bit of context:
> http://rickyclarkson.blogspot.com/2009/01/typeclass-pattern.html
>

This still does not allow you to write generic sections. I'm not
entirely sure but I think this is because in haskell numeric constants
are polymorphic:

 Prelude> :t 1
 1 :: (Num t) => t

while in scala they are monomorphic:

 scala> 1
 res0: Int = 1

This means in haskell the operation will drive the type of the constant
but in scala the constant will drive the type of the operation.

Hello,

In Haskell one can define a simple function like this:

Prelude> let add1 x = x + 1
Prelude> add1 2
3
Prelude> add1 2.0
3.0
Prelude> :type add1
add1 :: (Num a) => a -> a

Would it be possible to do the same thing in Scala? I mean:
def add1[U <% Number[U]](x:U) = x + 1

I made several attempt to define a trait Number[A] like in Ordered[A] but all of them failed. I guess if it was easy it would already be there...

Thanks,
Sebastien

Couldn't you just use a structural type?
Something like
def add1[T](v: { def +(T):T }):T = v + 1

(Not entirely sure about the syntax...
BR,John
On Fri, Jan 9, 2009 at 12:26 AM, Sebastien Bocq <sebastien.bocq@gmail.com> wrote:

Hello,

In Haskell one can define a simple function like this:

Prelude> let add1 x = x + 1
Prelude> add1 2
3
Prelude> add1 2.0
3.0
Prelude> :type add1
add1 :: (Num a) => a -> a

Would it be possible to do the same thing in Scala? I mean:
def add1[U <% Number[U]](x:U) = x + 1

I made several attempt to define a trait Number[A] like in Ordered[A] but all of them failed. I guess if it was easy it would already be there...

Thanks,
Sebastien