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?
We certainly were aware. It is a problem, and a big one. The monomorphism restriction (MR) was (barely) acceptable in Haskell 98 because at least the final value returned by the program was not changed by this kludge kicking in. But, as we point out in the paper, implicit parameters and the MR are simply incompatible. One of them has to go. As John Hughes intimated, this debate is part of a much larger issue as to how Haskell handles type schemes versus types, and implicit parameters show that type schemes can arise from causes other than polymorphism. In the long term, should Haskell maintain a distinction between types and type schemes? Between call-by-name and call-by-need? Should type schemes be permitted everywhere? If so, should inference do it's best and simply report when ambiguities arise? Etc. etc. I think the time has come for us to address these types of questions from a fundamental basis, not simply as fixes to the existing infrastructure. Otherwise we'll never be able to budge from the sludge of the kludge... John