[Haskell-cafe] some ideas for Haskell', from Python

[Lennart Augustsson]

Yes, the Agda modules remind me of Cayenne. :)

On Tue, Jan 20, 2009 at 12:54 PM, Bas van Dijk <v.dijk.bas at gmail.com> wrote:
> On Wed, Jan 14, 2009 at 3:59 PM, Manlio Perillo
> <manlio_perillo at libero.it> wrote:
>> 2) In Python it is possible to import modules inside a function.
>>
>>   In Haskell something like:
>>
>>   joinPath' root name =
>>       joinPath [root, name]
>>       importing System.FilePath (joinPath)
>
> I just like to point out the dependently typed, Haskell-like,
> programming language Agda[1] which has a very nice module system with
> the following features:
>
>  * Modules can contain other modules
>
>  * Modules can be locally opened. For example:
>   mapMaybe f m = let open Maybe in maybe nothing (just . f) m
>
>  * Renaming of important names: For example:
>   open Maybe renaming (Maybe to option; nothing to none; just to some)
>
>  * Parameterized modules: For example:
>
>   module Sort (A : Set) (_<_ : A -> A -> Bool) where
>     insert : A -> List A -> List A
>     insert y [] = y :: []
>     insert y (x :: xs) with x < y
>     ... | true  = x :: insert y xs
>     ... | false = y :: x :: xs
>
> See section 2.7 of the following Agda tutorial (an open minded Haskell
> hacker should be able to read that section on its own):
>
> http://www.cs.chalmers.se/~ulfn/darcs/AFP08/LectureNotes/AgdaIntro.pdf
>
> Hopefully Haskell can borrow some of these ideas sometime.
>
> regards,
>
> Bas
>
> [1] http://wiki.portal.chalmers.se/agda/
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