import std.variant : Algebraic, This, visit;

import std.typecons : Tuple, tuple;

​

struct Nil

{

}

​

alias List(T) = Algebraic!(Nil, Tuple!(T, "head", This*, "tail"));

alias Cons(T) = Tuple!(T, "head", List!T*, "tail");

​

List!T* list(T)(T[] items...)

{

    if (items.length == 0)

        return new List!T(Nil());

    else

        return new List!T(Cons!T(items[0], list(items[1 .. $])));

}

​

string list2string(T)(List!T list)

{

    import std.stdio : write;

​

    list.visit!((Nil _) => "nil",

            (Cons!T cons) => "cons(" ~ cons.head ~ ", " ~ list2string(*cons.tail) ~ ")");

}

​

unittest

{

    List!int* myList = list(1, 2, 3);

​

    assert(list2string(*myList) == "cons(1, cons(2, cons(3, nil)))");

}