[Haskell-cafe] looking for examples of non-full Functional
Dependencies
Hans Aberg
haberg at math.su.se
Fri Apr 25 07:21:20 EDT 2008
On 18 Apr 2008, at 20:04, Martin Sulzmann wrote:
> Let's consider our running example
>
> class D a b | a -> b
> instance D a b => D [a] [b]
>
> which we can write in CHR notation
>
> D a b, D a c ==> b=c (FD)
>
> D [a] [b] <=> D a b (Inst)
>
> These rules overlap.
I experimented with translations into GNU Prolog (gprolog). Since "="
is hard to get working in Prolog unless integrated into unification,
I tried (using the idea of rewriting unique existence as functions,
possible if one assumes the axiom of choice):
class(d, A, b(A)).
instance(d, l(A), l(B)) :- class(d, A, B).
Then:
?- instance(d, l(A), l(B)).
B = b(A)
?- instance(d, l(A), C).
C = l(b(A))
?- instance(d, l(A), l(B)), instance(d, l(A), C).
B = b(A)
C = l(b(A))
Though I am not sure about the intended semantics, it does produce
unique solutions.
Hans
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