C++ Expression templates in ATS2

[Artyom Shalkhakov]

Here is my attempt to convert some C++ template metaprogramming approaches to ATS2, in particular, expression templates:

https://github.com/ashalkhakov/ATS-playground/blob/master/exptmp.dats

It seems to work (also, there is no dispatching happening at runtime, just as it doesn't in C++). However, I found that types must be distinct for using them to represent different nodes of the syntax tree. For instance, if Tid is [assume]d to be a double, the code compiles and runs, but produces undesired results.

Also, I'm wondering if C++ references can be mimicked in ATS2? Currently, the subtrees are embedded by value, instead of by reference. I'd like to avoid GC.

As a side-effect, looks like I'm finally starting to comprehend how C++ templates work by comparing to ATS. :)

[gmhwxi]

Nice!

The example typechecks. But how to run it?

[Artyom Shalkhakov]

On Saturday, March 14, 2015 at 9:05:54 PM UTC+6, gmhwxi wrote:

Nice!

The example typechecks. But how to run it?

I just do:

patscc exptmp.dats

And then:

./a.out

If you run it, it will print some results into console.

I didn't bother to create a proper makefile at this point.
 

[gmhwxi]

I like this example. I tidied it up:

https://github.com/githwxi/ATS-Postiats-test/blob/master/contrib/hwxi/TEST0/exptmp.dats

On Saturday, March 14, 2015 at 9:24:40 AM UTC-4, Artyom Shalkhakov wrote:

[gmhwxi]

It seems to work (also, there is no dispatching happening at runtime, just as it doesn't in C++). However, I found that types must be distinct for using them to represent different nodes of the syntax tree. For instance, if Tid is [assume]d to be a double, the code compiles and runs, but produces undesired results.

This is due to incorrect use of abstract types. See my code:

https://github.com/githwxi/ATS-Postiats-test/blob/master/contrib/hwxi/TEST0/exptmp.dats

Also, I'm wondering if C++ references can be mimicked in ATS2? Currently, the subtrees are embedded by value, instead of by reference. I'd like to avoid GC.

I don't quite understand the question. As it stands now, the code involves no memory allocation. When 'eval' is called, an expression value (a flat record) is passed
by reference.

 
On Saturday, March 14, 2015 at 9:24:40 AM UTC-4, Artyom Shalkhakov wrote:

[Artyom Shalkhakov]

On Sunday, March 15, 2015 at 7:42:44 AM UTC+6, gmhwxi wrote:

It seems to work (also, there is no dispatching happening at runtime, just as it doesn't in C++). However, I found that types must be distinct for using them to represent different nodes of the syntax tree. For instance, if Tid is [assume]d to be a double, the code compiles and runs, but produces undesired results.

This is due to incorrect use of abstract types. See my code:

https://github.com/githwxi/ATS-Postiats-test/blob/master/contrib/hwxi/TEST0/exptmp.dats

Thanks! Much better this way. Oh I see, I forgot to define the size of the abstract type.
 

Also, I'm wondering if C++ references can be mimicked in ATS2? Currently, the subtrees are embedded by value, instead of by reference. I'd like to avoid GC.

I don't quite understand the question. As it stands now, the code involves no memory allocation. When 'eval' is called, an expression value (a flat record) is passed
by reference.

Taking Esub_(E1:t@ype, E2:t@ype) = @(E1, E2) as example, both E1 and E2 are flat.

The C++ version would use [const E1&] and [const E2&] as the types for values, instead of E1 and E2 (so, it would use C++ references aka non-null pointers).
 

[gmhwxi]

See:

https://github.com/githwxi/ATS-Postiats-test/blob/master/contrib/hwxi/TEST0/exptmp_ref.dats

This one involves memory allocation. If an expression to be evaluated is known at compile-time,
then it can be constructed using static allocation.

[Artyom Shalkhakov]

On Sunday, March 15, 2015 at 10:19:40 AM UTC+6, gmhwxi wrote:

See:

https://github.com/githwxi/ATS-Postiats-test/blob/master/contrib/hwxi/TEST0/exptmp_ref.dats

This one involves memory allocation. If an expression to be evaluated is known at compile-time,
then it can be constructed using static allocation.

Thank you. By "static allocation", do you mean something like an approach given in Chapter 8 of Introduction to Programming in ATS, "Constructing a Statically Allocated List"?
 

[Hongwei Xi]

By "static allocation", do you mean something like an approach given in Chapter 8 of Introduction to Programming in ATS, "Constructing a Statically Allocated List"?

Yes.

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