Implicit Parameters

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
> 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 ;-)