Hi Fermin,
| Should redundant dependencies trigger an error or a warning? I'd
| say that if I'm writing some haskell code, I wouldn't mind if a
| redundancy is flagged as an error; most likely, it'd take a short
| time to fix. However, if someone is generating haskell automatically
| (maybe with Derive, PolyP, a GUI designer, ...), the easiest thing
| to do is to generate all the dependencies that will make the types
| correct, without trying to avoid redundancies. In this case,
| I think a warning is better.
Generating a warning instead of an error might indeed be
preferable. But I disagree with your motivation. Except in
cases where a language is specifically designed to be used as
a target such programs, I believe that implementations should
be optimized for the benefit of their human users. For the
comparatively rare cases where someone is writing a program
that generates Haskell class definitions, including dependencies,
it surely isn't too much to expect them to add a line or two to
filter out any that are redundant? After all, they are probably
having to work much harder just to pretty print the rest of the
text.
A better solution still would be to have a standardized library
called HaskellSyntax, which all of the code generating tools that
you describe (and more!) could use. The module would export a
set of datatypes for describing the abstract syntax of Haskell
programs and an associated set of pretty printers. (Or perhaps
the printer functions by themselves would be enough?) The pretty
printers would take care of all those minor little issues like
deciding when parentheses were needed, when an operator should
be written with applicative or infix syntax, breaking long strings
across line boundaries, etc. It could also take care of filtering
out redundant dependencies, for example, if this was considered
useful. I think this would be a neat library to have around,
especially if the authors of tools like Derive, PolyP, H/Direct,
Happy, or anything else that generates Haskell code could be
persuaded to use it. I hope somebody will take up the challenge!
All the best,
Mark
