Diagrams for types; unit vs void?

[Brandon Barker]

I find the following diagram helpful to sort of know what's what in Scala: https://www.scala-lang.org/old/node/128.html

Now, ATS is very different, I'm not sure such a diagram could even make sense (it isn't a language that deals with subclassing much as I understand it). But if anything like it is possible (and maybe more than one diagram is necessary), I think it could be helpful to place these early on in one of the ATS documentation sections/books.

Now I get the sense that ATS's void is actually the unit type, is this correct? What is the uninhabited type in ATS, if any?

[Hongwei Xi]

ATS's void is unit. The name 'void' refers to the fact that the memory needed

for the void-value is 0 bytes. Unfortunately, there is no type in C of 0 size (I did

try struct{}). This is the place where a theorist and an engineer differ fundamentally.

One really needs a theorist's C in order to compile ATS faithfully.

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[Hongwei Xi]

There are many uninhabited types in ATS.

For instance ([false] void) is such a type. Or you can use {a:type} a

(that is, forall a. a).

On Sat, Mar 10, 2018 at 9:35 AM, Brandon Barker <brandon...@gmail.com> wrote:

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[Brandon Barker]

Ah, interesting - to get around that, does ATS just translate every void value assiagnment as the execution of a C function call returning void?

On Saturday, March 10, 2018 at 9:44:34 AM UTC-5, gmhwxi wrote:

ATS's void is unit. The name 'void' refers to the fact that the memory needed

for the void-value is 0 bytes. Unfortunately, there is no type in C of 0 size (I did

try struct{}). This is the place where a theorist and an engineer differ fundamentally.

One really needs a theorist's C in order to compile ATS faithfully.

On Sat, Mar 10, 2018 at 9:35 AM, Brandon Barker <brandon...@gmail.com> wrote:

I find the following diagram helpful to sort of know what's what in Scala: https://www.scala-lang.org/old/node/128.html

Now, ATS is very different, I'm not sure such a diagram could even make sense (it isn't a language that deals with subclassing much as I understand it). But if anything like it is possible (and maybe more than one diagram is necessary), I think it could be helpful to place these early on in one of the ATS documentation sections/books.

Now I get the sense that ATS's void is actually the unit type, is this correct? What is the uninhabited type in ATS, if any?

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[Hongwei Xi]

Pretty much so.

Sometimes, not being able to have values of 0 bytes causes wastefulness.

For instance, a map from keys to items becomes a set if the items are of the

type void. If I write code like this, the code can pass typechecking but is to be

stopped by the C compiler. Instead, I have to use integer 0 as a dummy item

but doing so wastes memory and CPU cycles.

I read that ancient Romans did not have a numeral for zero. By that, you could

infer that they were a very pratical people :)

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[Yannick Duchêne]

Le samedi 10 mars 2018 15:44:34 UTC+1, gmhwxi a écrit :

ATS's void is unit. The name 'void' refers to the fact that the memory needed

for the void-value is 0 bytes. Unfortunately, there is no type in C of 0 size (I did

try struct{}). This is the place where a theorist and an engineer differ fundamentally.

One really needs a theorist's C in order to compile ATS faithfully.

I just wondered about the status of `void` after this:

        fn f(void): int = 0

… it does not compile and the same with `unit`. Only this do:

         fn f(): int = 0

After that comment, I guess it’s half‑intended and half‑not.

[Yannick Duchêne]

By the way, what was the issue with an empty struct? No really empty?

[Hongwei Xi]

For instance, gcc does not support an empty struct.

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