• Meta (29/29) Apr 27 2014 I'm trying to create a basic List type using Algebraic, but the
• bearophile (7/9) Apr 27 2014 As stated in its docs, Algebraic is not yet finished and good for
• Meta (3/12) Apr 27 2014 Is it necessary to use This[]? I tried changing it to This* and
• Meta (6/8) Apr 27 2014 I should specify. This did not work:
• bearophile (6/11) Apr 27 2014 An Algebraic is a sum type, so you can't store two value in it,
• Meta (13/18) Apr 27 2014 Ah, you're right. I'm getting mixed up from my own initial
• bearophile (8/11) Apr 27 2014 Algebraic is currently unfinished and needs improvements. If it
• bearophile (5/6) Apr 27 2014 Also your Cons seems a value type, like Algebraic itself. You
• Meta (3/9) Apr 27 2014 Yes, it's hard to figure out Algebraic's particular kind of

"Meta" <jared771 gmail.com> writes:

I'm trying to create a basic List type using Algebraic, but the 
compiler keeps complaining about recursive aliasing.

import std.variant;

struct Cons(T, U: List)
{
	public static opCall(T t, U u)
	{
	}
}

//Error
alias List = Algebraic!(typeof(null), Cons!(int, This));

void main()
{
	List l = Cons(1, Cons(2, Cons(3, null)));
}

I tried changing Cons like so:


struct Cons(T, U)
{
     //...
}

Then I get:
Error: struct f809.Cons cannot deduce function from argument types
!()(int, typeof(null)), candidates are: f809.Cons(T, U)

Error: struct std.variant.This unknown size
Error: struct std.variant.This unknown size
Error: variable f809.Cons!(int, This).Cons.opCall.u no definition 
of struct This

I'm not sure what else I could try. Does anyone have any advice 
on using this?

"bearophile" <bearophileHUGS lycos.com> writes:

Meta:

 I'm trying to create a basic List type using Algebraic, but the 
 compiler keeps complaining about recursive aliasing.

As stated in its docs, Algebraic is not yet finished and good for 
recursive data structures. But here I have put an usage example 
of that kind:

http://rosettacode.org/wiki/Flatten_a_list#With_an_Algebraic_Data_Type

Bye,
bearophile

"Meta" <jared771 gmail.com> writes:

On Sunday, 27 April 2014 at 20:22:12 UTC, bearophile wrote:
 Meta:

 I'm trying to create a basic List type using Algebraic, but 
 the compiler keeps complaining about recursive aliasing.

 As stated in its docs, Algebraic is not yet finished and good 
 for recursive data structures. But here I have put an usage 
 example of that kind:

 http://rosettacode.org/wiki/Flatten_a_list#With_an_Algebraic_Data_Type

 Bye,
 bearophile

Is it necessary to use This[]? I tried changing it to This* and 
it blew up on me.

"Meta" <jared771 gmail.com> writes:

On Sunday, 27 April 2014 at 20:38:37 UTC, Meta wrote:
 Is it necessary to use This[]? I tried changing it to This* and 
 it blew up on me.

I should specify. This did not work:

alias T = Algebraic!(int, This*);

void main() {
	auto l = T(1, new T(2, new T(3, null)));
}

"bearophile" <bearophileHUGS lycos.com> writes:

Meta:

 I should specify. This did not work:

 alias T = Algebraic!(int, This*);

 void main() {
 	auto l = T(1, new T(2, new T(3, null)));
 }

An Algebraic is a sum type, so you can't store two value in it, 
only one, an int or a T*. But this is not going to solve your 
problems...

Bye,
bearophile

"Meta" <jared771 gmail.com> writes:

On Sunday, 27 April 2014 at 20:54:02 UTC, bearophile wrote:
 An Algebraic is a sum type, so you can't store two value in it, 
 only one, an int or a T*. But this is not going to solve your 
 problems...

 Bye,
 bearophile

Ah, you're right. I'm getting mixed up from my own initial 
example. Fiddling with it a bit brings me back around to your 
code:

import std.variant;

alias List = Algebraic!(int, This[]);

void main()
{
	List l = List([List(1), List([List(2)])]);
}

Which is absolutely ugly. The more I try to use Algebraic, the 
more I come to think that this is something that can't be done 
cleanly in a library, even in D.

"bearophile" <bearophileHUGS lycos.com> writes:

Meta:

 The more I try to use Algebraic, the more I come to think that 
 this is something that can't be done cleanly in a library, even 
 in D.

Algebraic is currently unfinished and needs improvements. If it 
turns out it's not possible to implement it well in library code, 
we can find the minimal core language additions needed to 
implement it well, and ask for them :) D is not set in stone 
regarding additive changes.

Bye,
bearophile

"bearophile" <bearophileHUGS lycos.com> writes:

Meta:

 alias List = Algebraic!(typeof(null), Cons!(int, This));

Also your Cons seems a value type, like Algebraic itself. You 
have to avoid creating an infinite-size algebraic value.

Bye,
bearophile

"Meta" <jared771 gmail.com> writes:

On Sunday, 27 April 2014 at 20:28:28 UTC, bearophile wrote:
 Meta:

 alias List = Algebraic!(typeof(null), Cons!(int, This));

 Also your Cons seems a value type, like Algebraic itself. You 
 have to avoid creating an infinite-size algebraic value.

 Bye,
 bearophile

Yes, it's hard to figure out Algebraic's particular kind of 
"magic".