Is () a 0-length tuple?
|
View:
New views
14 Messages
—
Rating Filter:
Alert me
|
 |
Is () a 0-length tuple?
by Pasqualino "Titto" Assini
::
Rate this Message:
Hi,
I just noticed that the json library maps () to a JSON empty array: []. This makes sense if () is a 0-length tuple, the (2,"hi") tuple for example maps to [2,"hi"] But is it so in Haskell? In what sense () is a 0-length tuple? Thanks, titto _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Ross Mellgren
::
Rate this Message:
It is kind of a 0-length tuple, if you squint, though it's usually
called "unit". Each tuple type is entirely distinct from each other, so there's nothing that indicates that something is a tuple except for the spelling -- (a,b,c). For example, unlike python, there is no way to determine the length of a tuple at runtime (e.g. length ()) nor iterate at runtime (as the types are heterogeneous). -Ross On Nov 6, 2009, at 5:08 PM, Pasqualino Titto Assini wrote: > Hi, > > I just noticed that the json library maps () to a JSON empty array: > []. > > This makes sense if () is a 0-length tuple, the (2,"hi") tuple for > example maps to [2,"hi"] > > But is it so in Haskell? > > In what sense () is a 0-length tuple? > > Thanks, > > titto > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@... > http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by John Dorsey-2
::
Rate this Message:
> 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@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
|
|
|
Re: Is () a 0-length tuple?
by jkff
::
Rate this Message:
2009/11/7 Pasqualino "Titto" Assini <tittoassini@...>:
> 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 <haskell@...>: >>> 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@... >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > > -- > Pasqualino "Titto" Assini, Ph.D. > http://quicquid.org/ > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@... > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Eugene Kirpichov Web IR developer, market.yandex.ru _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
|
|
|
Re: Is () a 0-length tuple?
by Ketil Malde-5
::
Rate this Message:
Eugene Kirpichov <ekirpichov@...> writes:
>> 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., _|_). I'd argue that yes, they're the same thing, since any function returning "null" in JS might also fail to terminate or terminate with an exception. -k -- If I haven't seen further, it is by standing in the footprints of giants _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Svein Ove Aas
::
Rate this Message:
On Sun, Nov 8, 2009 at 9:52 AM, Ketil Malde <ketil@...> wrote:
> Eugene Kirpichov <ekirpichov@...> writes: > >>> 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., _|_). > How should I put it..? undefined is bottom, but bottom is not undefined? There are plenty of other constructions that are bottom. Infinite loops, throws, errors.. common for all of them, of course, is that you can't pattern-match on them or otherwise use them in pure code, and they generally don't act like values. So, can't we just say that () has a single value, namely ()? It'd make this much simpler, and we won't have to deal with the Nihil monoid. == data Nihil instance Monoid Nihil where mappend _ _ = undefined -- Svein Ove Aas _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Conor McBride-2
::
Rate this Message:
How about this?
{-# LANGUAGE ThinkTotal #-} On 8 Nov 2009, at 09:53, Svein Ove Aas wrote: > On Sun, Nov 8, 2009 at 9:52 AM, Ketil Malde <ketil@...> wrote: >> Eugene Kirpichov <ekirpichov@...> writes: >> >>>> 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., _|_). () is the only value of (). If we could agree a standard set of email pragmas, we could save ourselves a lot of violent agreement. Cheers Conor _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Fwd: Is () a 0-length tuple?
by Jon Fairbairn
::
Rate this Message:
"Pasqualino \"Titto\" Assini" <tittoassini@...> 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@... _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Deniz Dogan-3
::
Rate this Message:
2009/11/7 Matthew Gruen <wikigracenotes@...>:
> Forgot to cc haskell-cafe. Trying again: > > ---------- Forwarded message ---------- > From: Matthew Gruen <wikigracenotes@...> > Date: Sat, Nov 7, 2009 at 2:16 PM > Subject: Re: [Haskell-cafe] Is () a 0-length tuple? > To: Pasqualino Titto Assini <tittoassini@...> > > On Sat, Nov 7, 2009 at 2:00 PM, Pasqualino "Titto" Assini > <tittoassini@...> 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 > JavaScript. > > 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. What point are you trying to make by distinguishing JSON from JavaScript? JSON is a subset of JavaScript, they share the same type system. "Null can be only one value." This doesn't make sense to me, since as you say null is not a type, but a value. -- Deniz Dogan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Re: Fwd: Is () a 0-length tuple?
by Ketil Malde-5
::
Rate this Message:
Jon Fairbairn <jon.fairbairn@...> writes:
> The "empty" type in Haskell would be (forall a.a) which has no > non-bottom values. With an extension, you can also define: data Void -- without any constructors which is perhaps closer to null types in other languages? -k -- If I haven't seen further, it is by standing in the footprints of giants _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Matthew Gruen
::
Rate this Message:
On Sun, Nov 8, 2009 at 6:21 AM, Deniz Dogan <deniz.a.m.dogan@...> wrote:
> What point are you trying to make by distinguishing JSON from > JavaScript? JSON is a subset of JavaScript, they share the same type > system. "Null can be only one value." This doesn't make sense to me, > since as you say null is not a type, but a value. > > -- > Deniz Dogan > It seems I underestimated the typedness of null in JavaScript :) I checked the ECMAScript specification, and it does refer to a "null type".. so titto was right.[1] My opinion is that JSON's 'type system' should be analyzed orthogonal to JavaScript's regardless. If JSON is a subset of JavaScript, it is primarily a syntactic one. When I said "Null can be only one value", implying that null is a type, I was referring to JSON's null, not JavaScript's null. In JSON, null *is* definitely a unit type. When considering mappings between Haskell and JSON in the case of (), we should see that () is a unit type in Haskell, null is a unit type in JSON (regardless of its role in JavaScript), and maybe try to associate them. —Matt [1] I was misled by the fact that typeof null = 'object'. The logic behind this, I think, is that null is meant to be bound to a variable that would otherwise be a reference to an actual object value. Many have criticized this result, e.g. Douglas Crockford (http://javascript.crockford.com/remedial.html) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
|
|
Re: Is () a 0-length tuple?
by Deniz Dogan-3
::
Rate this Message:
2009/11/8 Matthew Gruen <wikigracenotes@...>:
> On Sun, Nov 8, 2009 at 6:21 AM, Deniz Dogan <deniz.a.m.dogan@...> > wrote: >> What point are you trying to make by distinguishing JSON from >> JavaScript? JSON is a subset of JavaScript, they share the same type >> system. "Null can be only one value." This doesn't make sense to me, >> since as you say null is not a type, but a value. >> >> -- >> Deniz Dogan >> > > It seems I underestimated the typedness of null in JavaScript :) I checked > the ECMAScript specification, and it does refer to a "null type".. so titto > was right.[1] My opinion is that JSON's 'type system' should be analyzed > orthogonal to JavaScript's regardless. If JSON is a subset of JavaScript, it > is primarily a syntactic one. When I said "Null can be only one value", > implying that null is a type, I was referring to JSON's null, not > JavaScript's null. In JSON, null *is* definitely a unit type. When > considering mappings between Haskell and JSON in the case of (), we should > see that () is a unit type in Haskell, null is a unit type in JSON > (regardless of its role in JavaScript), and maybe try to associate them. > > —Matt > > [1] I was misled by the fact that typeof null = 'object'. The logic behind > this, I think, is that null is meant to be bound to a variable that would > otherwise be a reference to an actual object value. Many have criticized > this result, e.g. Douglas Crockford > (http://javascript.crockford.com/remedial.html) > Let's keep in mind when reading the ECMAScript specification that JavaScript is merely based on it and breaks it on several different points. :) -- Deniz Dogan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@... http://www.haskell.org/mailman/listinfo/haskell-cafe |
| Free embeddable forum powered by Nabble | Forum Help |
