[Haskell-cafe] Eq Type Class: Overloading (==)
tom at confluent.org
Sun Sep 18 07:59:51 EDT 2005
Aaron Denney wrote:
> On 2005-09-17, Jason Dagit <dagit at eecs.oregonstate.edu> wrote:
>>A link to supertyping can be found here:
>>After reading that, I wonder why it's not implemented.
> Not enough people calling for it.
>>It seems like a wonderfully useful idea.
> It is. It would be terribly useful for those trying to prototype a
> new Prelude, and clean up the mathematical structures.
I like the idea of supertyping, but wouldn't that only allow you to
alter identifiers that were already classified? What about functions in
the Prelude that don't belong to a type class?
For instance, I have a datatype that needs an append-like operation, yet
it appears (++) is reserved only for lists.
I recently switched to Haskell from OCaml because I thought type classes
may solve one of my problems. I'm building an embedded language, which
has a lot of the basic operations. In OCaml I was forced to invent all
sort of obscure operator names for the embedded language so as not to
collide with the standard library.
But with Haskell's Num class, I have been able to reuse (+), (-), and
(*). However, (==) and (++) are still sticking points. My general
impression of Haskell is good, though it seems you're somewhat locked-in
by how the upper levels of the class hierarchy are defined in the
Prelude, or when the Prelude does not type class generic operator names
such as (++).
Again, I just stared programming Haskell. Please let me know if I'm
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