Interface and delegate D2.0

[Oliver Rübenkönig]

Hello Everyone,

the following code segment works. However, I am not sure I understand why it does work. Also, I have some questions regarding way I did it. 

I'd appreciate all sorts of comments you might have. Thanks.

---------------

import std.stdio;

//alias Expr delegate ( ) aFn; 
alias Expr delegate ( Expr ) aFn;

interface Expr {
    void print();
    aFn analize();
}

Expr eval( Expr e, Expr env ) {
    //return e.analize()();
    return e.analize()( env );
}

class String : Expr {
public:
    this( const char [] stringData )    { this.itsStringData = stringData; }
    void print()                        { writef("\"", this.itsStringData,"\""); }
    //aFn analize()                     { return { return cast(Expr)this; }; }
    aFn analize()                       { Expr help( Expr env ) {
                                                this.print();
                                                return cast(Expr)env; }
                                            return &help;
                                         }
private:
    const char [] itsStringData;
}

String makeString( const char [] stringData ) {
    return new String( stringData );
}

int main( char[][] arg ) {

    writefln();
    Expr s = makeString("Wow");
    Expr s2 = makeString("!");
    s.print();
    writefln();
    //s.analize()().print();
    s.analize()(s2).print();
    writefln();
    eval( s, s2 ).print();
    writefln();

    return 0;
}


---------------

1) In the String class is it possible to avoid the use of the "help" funcntion?
2) In the String class: why do I need to cast this to Expr - String is derived from Expr and should fit - should it not?
3) Is it possible to avoid the double brackets in Expr.analize()(Expr)? Something like Expr.analize(Expr)? I assume this could be done with an alias, are still the other ways? - well eval is another way. I think i am asking if you see a way to do the same  thing with less brackets.
4) Of course all other comments are very welcome!

Thanks for your help,
Oliver