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[Haskell-cafe] ANNOUNCE: repr-0.3.2

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Bas van Dijk

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Dec 23, 2009, 6:24:35 PM12/23/09
to Haskell Cafe
Hello,

Some months ago I uploaded a little package called 'repr' to hackage.
I've now updated the package to work with ghc-6.12.1 and its new base
library 4.2.0.0. Back then I forgot to make a proper announcement so I
will do that now:

'repr' allows you to render overloaded expressions to their textual
representation. For example:

*Repr> let rd = 1.5 + 2 + (3 + (-4) * (5 - pi / sqrt 6)) :: Repr Double
*Repr> show rd
"fromRational (3 % 2) + 2 + (3 + negate 4 * (5 - pi / sqrt 6))"

See: http://hackage.haskell.org/package/repr-0.3.2

regards,

Bas
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Andrey Sisoyev

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Dec 23, 2009, 7:00:38 PM12/23/09
to haskel...@haskell.org

Where do you make use of it? :)

Andrey
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Bas van Dijk

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Dec 24, 2009, 6:21:27 AM12/24/09
to Andrey Sisoyev, haskel...@haskell.org
On Thu, Dec 24, 2009 at 1:00 AM, Andrey Sisoyev
<Andrejs....@nextmail.ru> wrote:
> Where do you make use of it? :)

A few months ago I was working on 'levmar'[1] a Levenberg-Marquardt
data fitting library in Haskell. If you want your data fitting to be
really fast you need to supply a Jacobian of the model function you
want to fit. A Jacobian describes the partial derivatives of the
parameters of the model function. I used Conal Elliott's
vector-space[2] library to automatically derive a Jacobian from the
model function.

I was interested in the derivatives vector-space would come up with. A
derivative however, is just a function so the only thing you can do
with it is apply it to a value. This then yields a result which is
usually just a Double. I wasn't really interested in this actual
numeric result but more in the underlying numeric expressing that
generated that result.

So I wrote repr to visualize this numeric expression. However, after I
wrote repr, the work on levmar stalled a bit and I did not actually
get around to applying repr to the derivatives. I plan to make a new
release of levmar in the coming weeks or so and I think I will use
repr then.

regards,

Bas

[1] http://hackage.haskell.org/package/levmar
[2] http://hackage.haskell.org/package/vector-space

Lennart Augustsson

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Dec 24, 2009, 6:46:01 PM12/24/09
to Bas van Dijk, Andrey Sisoyev, haskel...@haskell.org
Did you consider using the traced package?

2009/12/24 Bas van Dijk <v.dij...@gmail.com>:

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