| title |
|---|
Datatype Generic Programming |
Today I had the pleasure of attending a talk by Andres
entitled "Datatype-Generic
Programming",
where Andres discussed how we can almost leverage the power of the
deriving construct for our own type classes.
Interestingly, this was a Haskell talk where I initially left thinking
that, while impressive there wasn't particularly a "wow" moment. But
then it hit me on the train back - the wow is really in the fact that
it's all so simple! Generic programming, at least with deriving Generic is straightforward, and the applications are immediately
obvious. It really helped that the talk was well paced, and I left
feeling I had a good understanding of the theory - switch over to an
isomorphic type representation with a limited set of constructors,
implement your type class there, and you can then provide wrappers to
use generic solutions.
The
generic-deriving
also got a mention towards the end of the talk, and it turns out this
is a library I've really been wanting. I was aware that it was
possible to write generic implementations of, for example, Monoid
for a while - but usually the overhead of writing a generic version
first was greater than just writing a single Monoid instance. I was
happy to find out that people have already done this hard work, so now
I just need to use the default implementations.
For example:
data Factory = Factory { trinkets :: Set Trinket
, widgets :: Set Widget
}
deriving (Generic)
instance Monoid Factory where
mappend = mappenddefault
mempty = memptydefaultDoes exactly what I want. Splendid.