[Haskell-cafe] Re: Aren't type system extensions fun? [Further analysis]

[Simon Peyton-Jones]

Andrew writes

| I have complete confidence that whoever wrote the GHC manual knew
| exactly what they meant. I am also fairly confident that this was the
| same person who implemented and even designed this particular feature.
| And that they probably have an advanced degree in type system theory. I,
| however, do not. So if in future the GHC manual could explain this in
| less opaque language, that would be most appreciated. :-}

As the person who wrote the offending section of the GHC user manual (albeit lacking a qualification of any sort in type theory), I am painfully aware of its shortcomings.  Much of the manual is imprecise, and explains things only by examples.  The wonder is that it apparently serves the purpose for many people.

Nevertheless, the fact is that it didn't do the job for Andrew, at least not first time around.

After some useful replies to his email, he wrote

| Thank you for coming up with a clear and comprehensible answer.

I would very much welcome anyone who felt able to improve on the text in the manual, even if it's only a paragraph or two.  If you stub your toe on the manual, once you find the solution, take a few minutes to write the words you wish you had read to begin with, and send them to me.

Meanwhile, Andrew, I recommend the paper "Practical type inference for arbitrary rank types", which is, compared to the user manual at least, rather carefully written.

Simon