Re: [Haskelldb-users] BoundedList ?

[Bjorn B. <bri...@cs...>]

On Jul 28, 2006, at 2:26 PM, Marc Weber wrote:

> I've tried understanding what the BoundedList.hs module is all =20
> about but
> I couldn' get it completely
>
> -- This inductive approach gives the complexity O(n) on the number =20
> of instances
> -- and very short type checking times compared to an O(n\^2) =20
> implementation.
>
> Where is the difference between [a] and (BoundedList a Nxx)?
> Is it only used for BoundedString by now?
> (to prevent data loss when copying from char(10) to char(4)?

Yes, BoundedList is only used for BoundedString in HaskellDB. The =20
purpose of BoundedString is, as you guessed, to avoid string =20
truncation. For more information, see our Haskell Workshop paper, =20
http://haskelldb.sourceforge.net/haskelldb.pdf

> Did I get it right that the internal representation is still an =20
> ordinary
> list ? (newtype BoundedList a n =3D BoundedList [a])?

Yes. BoundedList uses a phantom type to keep the string max length in =20=

the type of the list. The internal representation is a normal list.

> Looking at
>
> instance (Show a, Size n) =3D> Show (BoundedList a n) where
>     show l@(L xs) =3D show xs
>
> l@ is superfluous, isn't it?

Yes. There are probably lots of unused bindings in the HaskellDB =20
code. I guess we should compile with -Wall and fix all the warnings.

/Bj=F6rn