| I think the implementation is some 90% complete though, in GHC head.
| Certainly you can write many associated types programs already -- the
| missing part is finishing off associated type synonyms, iirc.
...and we have a working implementation of that too, thanks to Tom
Schrijvers. It's not in the HEAD yet, but it will be in a few weeks.
so it will be a part of 6.8? great news! afaiu, ATS, rather than AT,
is direct substitution for FD?
Functional dependencies desugar to indexed type families, an extension
of the original associated, in GHC head already. For the full story,
see the wiki page.
http://haskell.org/haskellwiki/GHC/Indexed_types
which includes an example of porting functional dependencies to
associated types
http://haskell.org/haskellwiki/GHC/Indexed_types#A_associated_type_synonym_example
It's really simple to replace a functional dependency with a type
function.
A class declaration
class C a b | a -> b
becomes:
class FD a ~ b => C a b where
type FD a
and an instance
instance C [x] x
becomes
instance C [x] x where
type FD [x] = x
That's it: only class and instance declarations have to be modified.
Now you can start to drop dependent parameters, if you want.
There are a few examples in my slides as well (if you don't mind
the pptx): http://www.cs.kuleuven.be/~toms/Research/talks/Tyfuns.pptx
Cheers,
Tom
--
Tom Schrijvers
Department of Computer Science
K.U. Leuven
Celestijnenlaan 200A
B-3001 Heverlee
Belgium
tel: +32 16 327544
e-mail: [EMAIL PROTECTED]
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