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

"Oliver Rübenkönig" <oliver.ruebenkoenigREM@web.de> wrote in message news:fr5epu$bos$1@digitalmars.com...
> 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;
> }
>
>
> ---------------

Firstly a disclaimer: the following comments are based on D2.012.

> 1) In the String class is it possible to avoid the use of the "help" funcntion?

You can make use of the following syntax:

    aFn analize()
    {
        return delegate Expr (Expr env) { this.print(); return env; }
    }

> 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?

I believe it's because the return type of the inline delegate is determined from your return statement. The syntax to define the return type is in the above example.

> 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.

I have the same gripe myself and haven't found any work around.

Neil

Neil Vice Wrote:

> Firstly a disclaimer: the following comments are based on D2.012.
> 
> > 1) In the String class is it possible to avoid the use of the "help" funcntion?
> 
> You can make use of the following syntax:
> 
>     aFn analize()
>     {
>         return delegate Expr (Expr env) { this.print(); return env; }
>     }
> 

that is exactly what i was looking for :-)

> > 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?
> 
> I believe it's because the return type of the inline delegate is determined from your return statement. The syntax to define the return type is in the above example.

OK.
> 
> > 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.
> 
> I have the same gripe myself and haven't found any work around.
> 

should you find something I'd be very interested. Thanks for you help.

Oliver