The only proper program I have tried to use hat on required rewriting to get hat to understand it. The program was only ~2k lines of code, and there were 3 different idiosyncrasies of hat which gave problems. The defaulting idiosyncrasy was one of them. It would be very helpful to know what the other problems were, apart from default numeric types. These three idiosyncrasies, if I recall correctly, required ~20 unwanted changes in my code, so I made a hat version of my code with these alterations, but it is very difficult to keep two parallel versions of a piece of code up to date with each other. For this reason, I didn't find it 'a slightly inconvenient problem'. I quite agree that maintaining parallel versions is a pain, and should be unnecessary. It is my personal belief that the lack of a powerful debugger/tracer that works 'straight out of the box', is the major constraint preventing the widespread adoption of haskell. You may well be right. Those of us who developed Hat had the aim that it would indeed work 'straight out of the box' for any Haskell 98
Tom, Thanks for reporting your Hat experience, albeit a negative one. For those of us who use Hat regularly, and get the results we need, it is easy to forget the problems that new users may face. program. It is clear that we have fallen short of that aim, and it is useful to have reports such as yours. We'd like to fix whatever problems prevent people from using Hat on their Haskell 98 programs.
Hat is free to use, and because of this, I feel I shouldn't be whining about problems with it. However, I feel that descriptions of Hat, for example in the communities and activities report, or on the hat website, should contain prominent and frank statements about its current limitations. As I say, your report of problems is welcome and helpful. As to the need for prominent and frank statements about limitations, these are already provided. One link from the main Hat web page is to the Bugs and Limitations page. But if you think there are further limitations that should be added to the list, do tell us.
Regards Colin Runciman