// written in the D programming language
// author: Timon Gehr

import std.stdio;
import std.conv;

class Lazy(T){
    T delegate() compute;
    this(T delegate() compute){this.compute=compute;}
    this(T value){this.value=value;}
    T value;
    final T opCall(){
        if(compute==null) return value;
        value=compute(), compute=null;
        return value;
    }
    auto opDispatch(string op,T...)(T args){return lz({return mixin("opCall()."~op)(args);});}
    final string toString(){return to!string(opCall());}
}

Lazy!T lz(T)(T delegate() compute){return new Lazy!T(compute);} // lazy
Lazy!T st(T)(T value){return new Lazy!T(value);}                // strict

template Type(S){alias typeof({S a;return a();}()) Type;}

struct List(T){
    Lazy!T head;
    Lazy!(List!T) tail;

    string toString(){
        if(empty) return "[]";
        char[] r=['['];
        for(auto xs=this;!xs.empty;xs=xs.tail()) r~=to!string(xs.head())~",";
        r[$-1]=']';
        return cast(string)r;
    }
    T front(){return head();}
    bool empty(){return head is null;}
    static List!T Empty;
    static this(){Empty=List!T(null,lz({assert(0,"Tried to get tail of empty list!");return List.init;}));}
    this(Lazy!T x, Lazy!(List!T) xs){
        head=x;
        tail=xs;
    }
    Lazy!T opIndex(int i){return drop(i-1,st(this))().head;}
    Lazy!(List!T) opSlice(int a,int b){return take(b-a,drop(a-1,st(this)));} //Bug? Cannot do LList!T;
}

auto cons(T)(Lazy!T x, Lazy!(List!T) xs){return lz({return List!T(x,xs);});}

//auto list(T)(Lazy!T[] args...){return lz({return List!T(args);});} // =O?
auto list(T)(Lazy!T[] args...){if(args==[]) return st(Empty!T); return cons(args[0],list(args[1..$]));}
auto list(T)(T[] args...) if(!is(T U==Lazy!U)){if(args==[]) return st(Empty!T); return cons(st(args[0]),list(args[1..$]));}

template Empty(T){alias List!T.Empty Empty;}
template LList(T){alias Lazy!(List!T) LList;}

LList!S map(T,S)(Lazy!S delegate(Lazy!T) f, Lazy!(List!T) xs){
    return lz({
            if(xs().empty) return Empty!S;
            return cons(f(xs.head), map(f,xs.tail))();
        });
}

LList!T filter(T)(Lazy!bool delegate(Lazy!T) p,Lazy!(List!T) xs){
    return lz({
            if(xs().empty) return Empty!T;
            auto rest=filter(p,xs.tail);
            if(p(xs.head)()) return cons(xs.head,rest);
            return rest;
        });
}

Lazy!S foldl(S,T)(Lazy!S delegate(Lazy!S,Lazy!T) f,Lazy!S nul,Lazy!(List!T) xs){
    return lz({
            if(xs().empty) return nul();
            return foldl(f,f(nul,xs.head), xs.tail)();
        });
}

Lazy!S foldlt(S,T)(Lazy!S delegate(Lazy!S,Lazy!T) f,Lazy!S nul,Lazy!(List!T) xs){
    return lz({
            auto a=nul;
            for(auto t=xs;!t().empty;t=t().tail) a=f(a,t.head);
            return a();
        });
}

Lazy!T foldr(S,T)(Lazy!T delegate(Lazy!S,Lazy!T) f,Lazy!T nul,Lazy!(List!S) xs){
    return lz({
            if(xs.empty) return nul();
            return f(xs.head,foldr(f,nul,xs.tail))();
        });
}

LList!T take(T)(int n,Lazy!(List!T) xs){
    return lz({
            if(n<=0) return Empty!T;
            return cons(xs().head,lz({return take(n-1,xs().tail)();}))();
        });
}

LList!T drop(T)(int n,Lazy!(List!T) xs){
    return lz({
            auto r=xs();
            foreach(i;0..n) r=r.tail();
            return r;
        });
}

LList!T zipWith(T,S,R)(Lazy!T delegate(Lazy!S,Lazy!R) f,Lazy!(List!S) xs, Lazy!(List!T) ys){
    return lz({
            if(xs().empty||ys().empty) return Empty!T;
            return cons(f(xs.head,ys.head),zipWith(f,xs.tail,ys.tail))();
        });
}

LList!(List!T) climbers(T)(Lazy!(List!T) xs){
    return lz({
            if(xs().empty) return Empty!(List!T);
            auto x=xs().head, ys=xs().tail;
            if(ys().empty) return list(list(x))();
            auto y=ys().head;
            if(x()>y()) return cons(list(x),climbers(ys))();
            auto zs=climbers(ys);
            return cons(cons(x,zs.head),zs.tail)();
        });
}

LList!T merge(T)(Lazy!(List!T) xs, Lazy!(List!T) ys){
    return lz({
            if(xs().empty) return ys();
            if(ys().empty) return xs();
            if(xs().head()<=ys().head()) return cons(xs.head,merge(xs.tail,ys))();
            return cons(ys.head,merge(xs,ys.tail))();
        });
}

LList!(List!T) mergepairs(T)(Lazy!(List!(List!T)) xss){
    return lz({
            if(xss().empty) return Empty!(List!T);
            if(xss().tail().empty) return xss();
            return cons(merge(xss.head,xss.tail().head),mergepairs(xss.tail().tail))();
        });
}

LList!T sort(T)(Lazy!(List!T) xs){
    LList!T loop(Lazy!(List!(List!T)) css){
        return lz({
                if(css().tail().empty) return css().head();
                return loop(mergepairs(css))();
            });
    }
    return lz({
            auto css=climbers(xs);
            return loop(css)();
        });
}

LList!ulong fibonacci()(){
    LList!ulong r;
    r=cons(st(1UL),cons(st(1UL),lz({return zipWith((Lazy!ulong a,Lazy!ulong b){return lz({return a()+b();});},r,r().tail)();})));
    return r;
}

LList!T naturals(T)(T start){
    return cons(st(start),lz({return naturals(start+1)();}));
}


import std.random;
void main(){
    writeln(take(93,fibonacci())());
    int[] a=new int[1000];
    foreach(ref x;a) x=uniform(0,cast(int)a.length);
    auto m=list(a);
    writeln(take(100,sort(m))());
}