>specify that a sort function (say) returns an ordered list
Fistly this is already possible in Haskell - see Oleg, Ralf and
My paper:
@misc{KLS04,
author = "Oleg Kiselyov and Ralf L{\"a}mmel and Keean Schupke",
title = "{Strongly typed heterogeneous collections}",
booktitle = "{ACM SIGPLAN Workshop on Haskell}",
year = 2004,
month = sep,
publisher = "ACM Press",
notes = "To appear"
}
http://homepages.cwi.nl/~ralf/HList/
Here we show constrained heterogeneous lists (but you can also
constrain the type in the list to turn it into a homogeneous list)
that includes the ability to impose ordering constraints...
Writing the constraint classes is a little involved but using it is
as simple as:
sort :: (HList l,HOrderedList l') => l -> l'
and supposing you dont like having to write the complete type, you
can use:
ordered :: HOrderedList l => l -> l
ordered = id
then you can use this in a function with no type given:
sort = ordered . sort'
So my point is this can be added to haskell _without_ breaking
any existing functionality - it is not either/or it is both/and!
Keean.
_______________________________________________
Haskell-Cafe mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell-cafe
