I've been wondering for a good while whether it's possible with what we have. Looks like it is, modulo some gnarly hacks in introspecting function types.

https://github.com/D-Programming-Language/phobos/pull/3394


Destroy!

Andrei

On Monday, 8 June 2015 at 07:51:24 UTC, Andrei Alexandrescu wrote:
> I've been wondering for a good while whether it's possible with what we have. Looks like it is, modulo some gnarly hacks in introspecting function types.
>
> https://github.com/D-Programming-Language/phobos/pull/3394
>
>
> Destroy!
>
> Andrei

Kind of like when I discovered this mail client written in awk, I'm both amazed and horrified.

On 6/8/15 1:51 AM, deadalnix wrote:
> On Monday, 8 June 2015 at 07:51:24 UTC, Andrei Alexandrescu wrote:
>> I've been wondering for a good while whether it's possible with what
>> we have. Looks like it is, modulo some gnarly hacks in introspecting
>> function types.
>>
>> https://github.com/D-Programming-Language/phobos/pull/3394
>>
>>
>> Destroy!
>>
>> Andrei
>
> Kind of like when I discovered this mail client written in awk, I'm both
> amazed and horrified.

Yah, the function parameter storage classes are gnarly to handle. The other type constructors line up quite nice. -- Andrei

On 06/08/2015 09:51 AM, Andrei Alexandrescu wrote:
> I've been wondering for a good while whether it's possible with what we
> have. Looks like it is, modulo some gnarly hacks in introspecting
> function types.
>
> https://github.com/D-Programming-Language/phobos/pull/3394
>
>
> Destroy!
>
> Andrei

- This is not alpha renaming. Alpha renaming renames a variable at the point it is bound and updates all occurrences of the variable. Alpha renaming does not change the term it is applied to. http://en.wikipedia.org/wiki/Lambda_calculus#.CE.B1-conversion
  This is type replacement.

- How do you use it to create recursive types using algebraic? (Assuming that's what your comment refers to.)

On 6/8/15 5:43 AM, Timon Gehr wrote:
> On 06/08/2015 09:51 AM, Andrei Alexandrescu wrote:
>> I've been wondering for a good while whether it's possible with what we
>> have. Looks like it is, modulo some gnarly hacks in introspecting
>> function types.
>>
>> https://github.com/D-Programming-Language/phobos/pull/3394
>>
>>
>> Destroy!
>>
>> Andrei
>
> - This is not alpha renaming. Alpha renaming renames a variable at the
> point it is bound and updates all occurrences of the variable. Alpha
> renaming does not change the term it is applied to.
> http://en.wikipedia.org/wiki/Lambda_calculus#.CE.B1-conversion
>    This is type replacement.

I'm using the term a bit loosely but I think appropriately.

> - How do you use it to create recursive types using algebraic? (Assuming
> that's what your comment refers to.)

I've added documentation and examples to http://erdani.com/d/phobos-prerelease/std_variant.html#.Algebraic. Feedback appreciated.


Thanks,

Andrei

On 06/08/2015 06:23 PM, Andrei Alexandrescu wrote:
> On 6/8/15 5:43 AM, Timon Gehr wrote:
>> On 06/08/2015 09:51 AM, Andrei Alexandrescu wrote:
>>> I've been wondering for a good while whether it's possible with what we
>>> have. Looks like it is, modulo some gnarly hacks in introspecting
>>> function types.
>>>
>>> https://github.com/D-Programming-Language/phobos/pull/3394
>>>
>>>
>>> Destroy!
>>>
>>> Andrei
>>
>> - This is not alpha renaming. Alpha renaming renames a variable at the
>> point it is bound and updates all occurrences of the variable. Alpha
>> renaming does not change the term it is applied to.
>> http://en.wikipedia.org/wiki/Lambda_calculus#.CE.B1-conversion
>>    This is type replacement.
>
> I'm using the term a bit loosely but I think appropriately.
> ...

Well, no, there is no binding site involved. You could use ReplaceType or SubstituteType.

>> - How do you use it to create recursive types using algebraic? (Assuming
>> that's what your comment refers to.)
>
> I've added documentation and examples to
> http://erdani.com/d/phobos-prerelease/std_variant.html#.Algebraic.
> Feedback appreciated.
> ...

Oh, it is used in the implementation. That clears it up.

Now, how do I declare mutually recursive types? :o)

>
> Thanks,
>
> Andrei
>

On Monday, 8 June 2015 at 07:51:24 UTC, Andrei Alexandrescu wrote:
> I've been wondering for a good while whether it's possible with what we have. Looks like it is, modulo some gnarly hacks in introspecting function types.
>
> https://github.com/D-Programming-Language/phobos/pull/3394
>
>
> Destroy!
>
> Andrei

almost missed the secondary(?) part of this PR.

http://erdani.com/d/phobos-prerelease/std_typecons.html#.ReplaceType

this looks incredibly useful, I often find myself using ugly templates to do this.