[Haskell-cafe] Using -> as both type and value constructor

[Daniel Fischer]

On Wednesday 24 August 2011, 20:24:14, Armando Blancas wrote:
> Studying the paper *A Simple Implementation for Priority Search Queues*,
> by Ralf Hinze, I came across the following syntax that I didn't
> understand and I couldn't use in GHCi 7.0.3 for defining a binding data
> type (page 3):
> 
> Bindings are represented by the following data type:
> *data k -> p = k -> p*
> key :: (k -> p) -> k
> key (k -> p) = k
> prio :: (k -> p) -> p
> prio (k -> p) = p
> Note that we use '->' both as a type constructor and value constructor.
> [...] data PSQ k p
> 
> The following page has these value constructors:
> 
> *0 :: PSQ k p*
> *{.} :: (k -> p) -> PSQ k p*
> 
> 
> The paper says that's Haskell '98 code.

I didn't see that claim in the linked slides, and it's not Haskell '98 (nor 
Haskell 2010).
There's a translation of the principles to Haskell from page 17 on or so.

> I'll appreciate info on what
> kind of data declaration those are and any pointers to related
> documentation. Or maybe those are deprecated features.

I don't think the notation from the beginning ever was legal Haskell, I 
think it was chosen to present the ideas separated from syntax.

> I'm stuck in this part.
> 
> -armando
> 
> www.cs.ox.ac.uk/people/ralf.hinze/talks/ICFP01.pdf