Jeffrey R. Lewis
Mon, 4 Feb 2002 09:00:02 -0800
On Monday 04 February 2002 01:58 am, Koen Claessen wrote:
> Hi all,
> Now we are talking about implicit parameters, let us take up
> the following problem with them on the Haskell mailing list
> [implicit parameters are not propogated down recursive definitions without
> a type signature]
> My questiona are: Were the designers of the implicit
> parameters paper aware of this problem when they wrote the
> paper? If so, they probably did not think this was a big
> problem. Do people in general think this is a problem?
I think we overlooked it when the paper was written, but I reported this at
the Haskell Implementers Meeting in Egmond. At the time the only solution
that occurred to me was to essentially do type inference twice - the first
time to figure out what implicit parameters the definition depends on, and
the second time with a weak signature provided that has those implicit
parameters on board to get the effect of the user having provided the
signature. I believe you guys have looked at something like this as well.
But I find that solution fairly unsatisfactory, and have been hoping
something nicer will come along....
I consider this to be a problem, but not enough of one that I've managed to
spend time finding a solution ;-)