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Today's Topics:
1. Re: Using a concept from Category Theory to enable you to
come back home after your function has taken you somewhere
(Brent Yorgey)
2. Re: Using a concept from Category Theory to enable you to
come back home after your function has taken you somewhere
(Miguel Negrao)
3. Re: DPH installation and LLVM (Erik de Castro Lopo)
----------------------------------------------------------------------
Message: 1
Date: Sun, 5 Aug 2012 08:37:30 -0400
From: Brent Yorgey <[email protected]>
Subject: Re: [Haskell-beginners] Using a concept from Category Theory
to enable you to come back home after your function has taken you
somewhere
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=iso-8859-1
On Sat, Aug 04, 2012 at 05:59:59PM +0000, Costello, Roger L. wrote:
>
> > How to automatically get the inverse of a Haskell function?
>
> That's a great question. I don't know the answer to that. Anyone else have an
> idea?
It is not possible in general... but on the other hand you can use
parametricity to pull some cool tricks. See Janis Voigtl?nder's paper
from 2009, "Bidirectionalization for free!"
(http://www.iai.uni-bonn.de/~jv/popl09-2.pdf) which is a fun read.
You can even play with an implementation of it here:
http://www-ps.iai.uni-bonn.de/cgi-bin/bff.cgi
-Brent
------------------------------
Message: 2
Date: Sun, 5 Aug 2012 14:05:58 +0100
From: Miguel Negrao <[email protected]>
Subject: Re: [Haskell-beginners] Using a concept from Category Theory
to enable you to come back home after your function has taken
you
somewhere
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252
Hi Roger,
A 04/08/2012, ?s 18:59, Costello, Roger L. escreveu:
> Hi Miguel,
>
> First note that I am very much a beginner at Category Theory. I am just
> sharing what I learn.
Yes I understand that, but what I was trying to say is that I don?t think that
this is much related with category theory.
>
>> How do you know that a Haskell function is injective? I don't think it's
>> possible to write a function which checks if another function is injective
>> or not .
>
> A function is injective if each input value (domain) yields a different
> output value (codomain). So if the set of inputs is finite, then it should be
> possible to write a function that loops over each input value and checks that
> its output is distinct from all other outputs.
Yes, but very few functions have finite domains, and if they do and it?s big it
would take a long time to test it. That is not a technique that can be used in
practice I think.
Brent wrote:
> It is not possible in general... but on the other hand you can use
> parametricity to pull some cool tricks. See Janis Voigtl?nder's paper
> from 2009, "Bidirectionalization for free!"
> (http://www.iai.uni-bonn.de/~jv/popl09-2.pdf) which is a fun read.
> You can even play with an implementation of it here:
>
> http://www-ps.iai.uni-bonn.de/cgi-bin/bff.cgi
>
> -Brent
Yes, I think that was the paper I had seen. Interesting stuff.
best,
Miguel Negr?o
------------------------------
Message: 3
Date: Mon, 6 Aug 2012 18:55:31 +1000
From: Erik de Castro Lopo <[email protected]>
Subject: Re: [Haskell-beginners] DPH installation and LLVM
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8
[email protected] wrote:
> Since I haven't gotten any further answers I'm trying my luck again?
>
> Does anyone have an idea how I can get the llvm backend to work? My
> configuration is:
>
> Mac OS X 10.7.4
> XCode 4.3.3 (with Command Line Tools installed)
> Haskell Platform 2012.2.0.0 32 bit
> llvm (via Homebrew)
DPH is not really a beginners topic. Maybe you should try the haskell-cafe
list.
Erik
--
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/
------------------------------
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