[Haskell-cafe] Announcing OneTuple-0.1.0

[Luke Palmer]

On Thu, Oct 2, 2008 at 1:17 AM, Simon Brenner <olsner at gmail.com> wrote:
> On 10/2/08, ajb at spamcop.net <ajb at spamcop.net> wrote:
>> G'day all.
>>
>>  Quoting John Dorsey <haskell at colquitt.org>:
>>
>>
>> > Contributions are welcome.  The project could use a tutorial, and a
>> > decent test suite.  Strict singleton tuples are planned for the next
>> > version.
>> >
>>
>>  I hope it has a Monad instance.
>
> You could always use this one-tuple instead and get Functor, Monad and
> MonadFix for free:
> http://hackage.haskell.org/packages/archive/mtl/1.1.0.1/doc/html/Control-Monad-Identity.html

But that one is different:

newtype Identity a = Identity { runIdentity :: a }
data OneTuple a = OneTuple { only :: a }

So OneTuple has one more value than Identity  (Identity Int has
Identity _|_ and Identity n for each n, whereas OneTuple Int has _|_,
OneTuple _|_, and OneTuple n for each n)

Luke