Hi folks, rather than discussing about which operator symbol to use for record access, which is really a question of personal taste we should try to seriously discuss the proposals and get to a solutions!
We all seem to agree that records are broken in Haskell. In order to fix that
we need a new and most probably incompatible solution. However, I think the
new solution should go in a new version of the Haskell standard (among other
things :-) ).
I would strongly disadvice to try to stick with the old system and improve it.
Just because there are lots of different opinions we should still try to find
a reasonable solution soon.
Desite the minor problem of '.' that dominated the discussion so far, what are
the REAL offences against Simons proposal [1] (denoted as SR in the
following)?
To me it sounds like a very reasonable starting point.
Which other proposals exist?
I quote David Roundy's list of problems [2] with a short annotation whether SR
solves them:
1. The field namespace issue.
solved by not sharing the same namespace with functions
2. Multi-constructor getters, ideally as a function.
not solved. only possible by hand
- As stated by Wolfgang Jeltsch [3] another datatype design might be
better
- I can image a solution is within SR example:
> data Decl = DeclType { name :: String, ... }
> | DeclData { name :: String, ... }
> | ...
> d :: Decl
in addition to
> d.DeclType.name
> d.DeclData.name
we provide (only if save, see 3.)
> d.name
3. "Safe" getters for multi-constructor data types.
not supported as it is
- with the above suggestion it could be possible (don't know if
desireable)
4. Getters for multiple data types with a common field.
- solved with contrains
> getx :: (r <: { x :: a }) => r -> a
5. Setters as functions.
doesn't seem to be supported, or I don't see it right now.
6. Anonymous records.
Supported
7. Unordered records.
I don' t understand it.
points added from me:
8. Subtyping
Supported, quite nicely
9. higher order versions for selecting, updateing ... [4]
not supported
seems important to me, any solutions?
Regards
Georg
[1] http://research.microsoft.com/~simonpj/Haskell/records.html
[2] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012226.html
[3] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012227.html
[4] http://www.haskell.org//pipermail/haskell-cafe/2005-November/012162.html
Am Donnerstag, 17. November 2005 19:08 schrieb Dimitry Golubovsky:
> Sebastian Sylvan wrote:
> >Personally I think that the dot is way to good of a symbol to be
> >"wasted" on function composition. I mean, how often do you really use
> >function composition in a way which doesn't obfuscate your code? I use
> >($) way more often than (.). Some people do use it more often than I
>
> I found it useful to use (mainly for debugging purposes)
>
> mapM (putStrLn . show) <some list>
>
> if I want to print its elements each on a new line.
>
> --
> Dimitry Golubovsky
>
> Anywhere on the Web
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