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 too.
[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 ;-) --Jeff