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digitalmars.D - Another kind of pointer arithmetic

reply Ianis Vasilev <ianis ivasilev.net> writes:
Somebody joked yesterday on Twitter about how pointer levels of 
indirection can be used to represent natural numbers and how we 
can do arithmetic with them (I can't find the post right now).

I decided to try and implement adding and multiplying levels of 
indirection:
https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde

I think it turned out fairly trivial.
Jun 26 2020
next sibling parent reply welkam <wwwelkam gmail.com> writes:
On Friday, 26 June 2020 at 14:00:27 UTC, Ianis Vasilev wrote:

 Somebody joked yesterday on Twitter about how pointer levels of 
 indirection can be used to represent natural numbers and how we 
 can do arithmetic with them (I can't find the post right now).

 I decided to try and implement adding and multiplying levels of 
 indirection:
 https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde

 I think it turned out fairly trivial.


This reminded me when one person heard that mov instruction is 
turing complete so he implemented c compiler that emitted only 
mov instructions
Jun 26 2020
parent Igor Shirkalin <isemsoft gmail.com> writes:
On Friday, 26 June 2020 at 18:18:34 UTC, welkam wrote:

 On Friday, 26 June 2020 at 14:00:27 UTC, Ianis Vasilev wrote:

 Somebody joked yesterday on Twitter about how pointer levels 
 of indirection can be used to represent natural numbers and 
 how we can do arithmetic with them (I can't find the post 
 right now).

 I decided to try and implement adding and multiplying levels 
 of indirection:
 https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde

 I think it turned out fairly trivial.


 This reminded me when one person heard that mov instruction is 
 turing complete so he implemented c compiler that emitted only 
 mov instructions


The task from the school:

Say, we have six intel 8086 cpu registers: ax, bx, cx, dx, si, 
di. Our task is to make the rotation: 
ah->al->bh->bl->ch->cl->dh->dl->ah. We can only use "move reg, 
reg" command. The si and di registers are undefined.
Jun 26 2020
prev sibling next sibling parent Stanislav Blinov <stanislav.blinov gmail.com> writes:
On Friday, 26 June 2020 at 14:00:27 UTC, Ianis Vasilev wrote:


 I decided to try and implement adding and multiplying levels of 
 indirection:
 https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde


int******

99 indirections on the wall...
Jun 26 2020
prev sibling parent reply Superstar64 <Hexagonalstar64 gmail.com> writes:
On Friday, 26 June 2020 at 14:00:27 UTC, Ianis Vasilev wrote:

 Somebody joked yesterday on Twitter about how pointer levels of 
 indirection can be used to represent natural numbers and how we 
 can do arithmetic with them (I can't find the post right now).

 I decided to try and implement adding and multiplying levels of 
 indirection:
 https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde

 I think it turned out fairly trivial.


This appears to be a form of peano numbers. See 
https://wiki.haskell.org/Peano_numbers
Jun 27 2020
parent reply Ianis Vasilev <ianis ivasilev.net> writes:
On Saturday, 27 June 2020 at 20:03:30 UTC, Superstar64 wrote:

 On Friday, 26 June 2020 at 14:00:27 UTC, Ianis Vasilev wrote:

 Somebody joked yesterday on Twitter about how pointer levels 
 of indirection can be used to represent natural numbers and 
 how we can do arithmetic with them (I can't find the post 
 right now).

 I decided to try and implement adding and multiplying levels 
 of indirection:
 https://gist.github.com/v--/5cbd0046be6fc5dbff9a9ad2f1717cde

 I think it turned out fairly trivial.


 This appears to be a form of peano numbers. See 
 https://wiki.haskell.org/Peano_numbers


Yes, the whole point was implementing the corresponding semigroup 
operations.

The nice thing is that D templates allow mapping combinations of 
types and values to other types and values, which allows for a 
lot of flexibility (this is not specific to D, but it is nice 
nonetheless). For example, the defined templates can be viewed as 
mappings (or morphisms, or whatever) with the following 
signatures:

IndirectionCounter: Types -> Values
Add: Types × Types -> Types
Mul: Types × Types -> Types

You can map types to values via IndirectionCounter, but you can 
also create types from values by implementing the inverse of the 
IndirectionCounter template.

I remember somebody talking about compile-time metaclasses some 
time ago, however I think that the type system is rich enough as 
it is right now.
Jun 27 2020
parent Ianis Vasilev <ianis ivasilev.net> writes:
On Saturday, 27 June 2020 at 23:16:37 UTC, Ianis Vasilev wrote:

 On Saturday, 27 June 2020 at 20:03:30 UTC, Superstar64 wrote:

 [...]


 Yes, the whole point was implementing the corresponding 
 semigroup operations.

 [...]


I meant semiring operations, sorry.
Jun 27 2020