2009/11/7 Pasqualino "Titto" Assini :

The syntax is similar, but what else is?

In JavaScript there is a "null" value, that is the only value of the null type.

Isn't () the same thing?  The only value of the unary type?

No, () has two values: () and undefined (t.i., _|_).

Best,

                titto

2009/11/6 John Dorsey :

...

...

In what sense () is a 0-length tuple?

In what sense isn't it?

Data.Tuple is much to narrow to be of any use here.  () is in at least most, if not all, of the type classes that tuples are in.  The syntax is strikingly similar.

If you ask me, it walks/quacks/smells like a duck, so it's a duck.

Regards, John

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Pasqualino "Titto" Assini, Ph.D. http://quicquid.org/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

-- Eugene Kirpichov Web IR developer, market.yandex.ru

"Pasqualino \"Titto\" Assini" writes:

The syntax is similar, but what else is?

What would you expect from an empty tuple? (a,b,c) has a constructor function p3 a b c = (a,b,c) and three destructor functions s3_1 (a,b,c) = a, s3_2 (a,b,c) = b and s3_3 (a,b,c)=c (a,b) has a constructor function p2 a b = (a,b) and two destructor functions s2_1 (a,b) = a and s2_2 (a,b) = b (a) has a constructor function p1 a = (a) and one destructor function s1_1 a = a () has a constructor function p0 = () and zero destructor functions.

In JavaScript there is a "null" value, that is the only value of the null type.

I'm not sure that Javascript is a suitable place to get intuitions for Haskell (null type would seem more like empty than single), but anyway, the thing is that the sole (non-bottom) value of the /unit/ type is the same as the empty tuple¹.

Isn't () the same thing?  The only value of the unary type?

The "empty" type in Haskell would be (forall a.a) which has no non-bottom values. [1] Aside: I wanted haskell to share the same type for all empty values (ie lists would have been symmetric unions of pairs with the unit type List t = (t,List t) || ()), but that didn't fit with algebraic datatypes so the design went a different way. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk