[Haskell-cafe] Is () a 0-length tuple?

Matthew Gruen wikigracenotes at gmail.com
Sat Nov 7 14:20:42 EST 2009

Forgot to cc haskell-cafe. Trying again:

---------- Forwarded message ----------
From: Matthew Gruen <wikigracenotes at gmail.com>
Date: Sat, Nov 7, 2009 at 2:16 PM
Subject: Re: [Haskell-cafe] Is () a 0-length tuple?
To: Pasqualino Titto Assini <tittoassini at gmail.com>

On Sat, Nov 7, 2009 at 2:00 PM, Pasqualino "Titto" Assini
<tittoassini at gmail.com> wrote:
> 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?
> Best,
>                 titto
> Pasqualino "Titto" Assini, Ph.D.
> http://quicquid.org/

In JavaScript's case, there is not a null type. The null value belongs
to the 'object' type, whereas the undefined value belongs to the
'undefined' type. This is all a lot less useful when you realize that
JavaScript has a dynamic type system. But this is JSON, not

In JSON, arrays, objects, strings, and numbers can be any number of
values. Booleans can be two values. Null can only be one value.
Personally, I think a better mapping for () would be JSNull, since
both have only one value in normal form. However, there is not
necessarily any natural mapping between Haskell values and JSON
values. The library tries to provide as many as possible, including
(), which it happens to map to JSArray [] instead of JSNull. As long
as the library is internally consistent, though, it should be fine.

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