"Pasqualino \"Titto\" Assini"
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