Is there any way to fix this elegant way to walk a tree at compile time?

[Gareth Charnock]

I was trying to walk a tree at compile time and I came up with this 
method. It seems very elegant, but unfortunately it fails with a 
recursive alias declaration error. I have a bad feeling there's no way 
to fix this but I thought I'd ask in case anyone had any ideas.

(https://gist.github.com/783832 for syntax highlighting, easier on the eye)

import std.typetuple;

template staticReduce(alias F,T...) {
        static if(T.length==0) {
                alias TypeTuple!() staticReduce;
        } else static if(T.length==1) {
                enum staticReduce=T[0];
        } else {
            enum 
staticReduce=staticReduce!(F,TypeTuple!(F!(T[0],T[1]),T[2..$]));
        }
}

template concan(string s1,string s2) {enum concan = s1 ~ s2;};
static assert(staticReduce!(concan,"Hello", " world")=="Hello world"); 
//passes


template Flatten(Tree,string s = "") {
        alias staticReduce!(concan,staticMap!(Flatten,Tree.ChildrenTuple)) 
Flatten;
}

struct TreeNode(Children...) {
        alias Children ChildrenTuple;
}

alias TreeNode!("A",TreeNode!("B","C","D"),"E") StaticTree;
static assert(Flatten!(StaticTree) == "ABCDE");
//Error: alias 
static_walk_tree.Flatten!(TreeNode!("A",TreeNode!("B","C","D"),"E")).Flatten 
recursive alias declaration