[nem-en] recursive types

[Wiktor Zychla]

thanks, I've already managed to find the () notation. I've adopted the 
"ignore(..)" stuff.

as you've noticed, I started the Nemerle adventure with simple Lambda 
Interpreter. I will not stop bothering you until I am not finished with it 
;)

frankly, trying to get used to Nemerle, I constantly fall into such traps. 
The "unbound member" is my favourite. I think that it should be revised or 
at last the compiler message MUST explain it better.

now I cannot compile following code. What could be wrong now?

unbound member `DummyName' in type `Lambda'
unbound member `Subsitute' in type `Lambda'

using System;
using System.Collections;

variant Lambda {
 | Abs { name : string; term : Lambda; }
 | App { term1 : Lambda; term2 : Lambda; }
 | Var { name : string;}

 static mutable DummyNo : int = 0;
 public static FreshName : string {
  get {
   string.Format( "dummy_{0}", ++DummyNo );
  }
 }

 Substitute( e : Lambda, x : string ) : Lambda {
  match( this ) {
   | Abs( name, term ) =>
    match( name ) {
     | x => Abs( name, term );
     | _ =>
      mutable dummyN = Lambda.DummyName;
      Abs( dummyN, this.Subsitute( Var(dummyN), name ).Substitute( e, x ) );
    }
   | App ( term1, term2 ) =>
    App( term1.Substitute( e, x ), term2.Substitute( e, x ) );
   | Var( name ) =>
    match( name ) {
     | x => e;
     | any => any;
    }
  }
 }
}

Wiktor