[Haskell-cafe] Name overloading

John Millikin jmillikin at gmail.com
Wed Jan 13 14:08:08 EST 2010

The usual suggestion I see for this sort of thing is to create a
typeclass for the operations you care about[1][2]. For example:

class HasOpen a where
  open :: a -> Handle

data DB
data FS

openDB :: DB -> Handle
openFS :: FS -> Handle

instance DB HasOpen where open = openDB
instance FS HasOpen where open = openFS

Of course, this doesn't allow you to have functions share the same
name if they have different signatures, as in your (open :: FS ->
File) example. To be honest, I think the C / Haskell approach of
unambiguously-identified functions is clearly superior to the C++ / C#
/ Java "class as namespace" idiom, which has caused me no end of

Dynamic languages such as Python and Ruby, of course, can return
anything from anywhere. This is nice in some cases, but having used
both extensively I think (static typing+inference) is a better
solution than dynamic typing.

> Now, in Haskell we have type inference, which is "The Good Thing" as
> it allows to "validate" your program at compile time. Hence, the idea
> coming up to my mind is that type inference actually forbids a
> type-directed resolution of names as in C++ or Java.
> Is this correct?

Type inference and static typing are separate; inference makes static
typing usable, but static typing makes compile-type correctness
verification easier. And it's not inference making your goal
impossible, but the fact that Haskell (like C) does not support
arbitrary overloading.

[1] http://www.mail-archive.com/haskell-cafe@haskell.org/msg64844.html
[2] http://stackoverflow.com/questions/1897306/haskell-record-syntax-and-type-classes

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