[Haskell-beginners] Can fields in a record be optional?

[Yitzchak Gale]

I wrote:
>> You don't need the added complexity of a type class for
>> this - just define the default value.

Michael Snoyman wrote:
> I don't think it's a case of necessity. It just happens to be very
> convenient to be able to use the three letters "def" instead of
> "defaultFrobnicatorSettings" or something like that.

You can use whatever name you'd like for a default value,
short or descriptive.

Type classes are a beautiful and powerful technique
in Haskell, but they do add some underlying complexity
to your types. In my experience, when building and
maintaining large code bases in Haskell, things are
much easier when you limit the use of type classes
to when they are really needed.

I create type classes when I need non-trivial polymorphism.
Even then, I often prefer simpler techniques such
as data types with parameters or passing functions as
parameters. There are also advanced techniques
using type classes which are needed for building some
kinds of libraries.

In particular, I have come to the conclusion that type classes
are not a good tool for simple namespace control in a typical
Haskell program.

It is a common mistake for beginners who come to Haskell
with a background in OOP to massively overuse type
classes.

Style is a matter of taste, of course. But much of the power
and beauty of Haskell lies away from type classes, and it's
a shame to miss out on it. So I think it is important for beginners,
especially when coming from OOP, to start out by avoiding
defining type classes whenever there is a good alternative
(i.e. almost always).

Regards,
Yitz