I'm trying to write a D implementation of Haskell's "type level
quicksort"[0], but I'm already running into problems with
std.typecons.Typedef. I have tried to translate this Haskell code:
data Zero
data Succ a
-- booleans
data True
data False
-- lists
data Nil
data Cons a b
-- shortcuts
type One = Succ Zero
type Two = Succ One
type Three = Succ Two
type Four = Succ Three
To this code in D:
import std.typecons;
struct Zero {}
struct Succ(a) {}
struct True {}
struct False {}
struct Nil {}
struct Cons(a, b) {}
alias One = Typedef!(Succ!Zero);
alias Two = Typedef!(Succ!One);
alias Three = Typedef!(Succ!Two);
alias Four = Typedef!(Succ!Three);
void main()
{
auto test = Four();
}
But I'm getting a compiler error when actually trying to
construct a Four:
Error: template std.typecons.Typedef!(Succ!(Zero),
Succ()).Typedef.Proxy!(Typedef_payload).opCall does not match any
function template declaration.
Candidates are:
std.typecons.Typedef!(Succ!(Zero),
Succ()).Typedef.Proxy!(Typedef_payload).opCall(this X,
Args...)(auto ref Args args)
I tried defining a static opCall in the Zero struct that doesn't
take any arguments, but that didn't make a difference. I'm
guessing this is a bug with Typedef, but does anyone have an idea
of where that bug might be?
1.
http://www.haskell.org/haskellwiki/Type_arithmetic#An_Advanced_Example_:_Type-Level_Quicksort
