Recursive definitions with variant - vilinski/nemerle GitHub Wiki

Recursive Definitions

Category: Defining Types
Description: Variants can be defined to give recursive collections of types.
Link: see Mutual definitions with records for example of use records as mutual recursive collections
Code:

 using System; 
 using System.Console;

// define mutually recursive collections with variants 
variant Connection 
{

    | Airport { Name : string; Connections : list[Connection]; }
    | None
           
    // prints contents of class
    public override ToString() : string
    {
        match (this)
        {
			// if it contains Airport
			| Airport(n, c) => $"Airport: Name = $n; Connections = $c"
			| _             => "no connection"
        }
    }

}

module RecursiveDefinition 
{

    Main() : void
    {
    def lax = Connection.Airport("Los Angeles Intl Airport", [Connection.None()]);
    // using named parameters in contructor
    def dtw = Connection.Airport(name = "Detroit Metro Wayne County", connections = [Connection.None()]);
    def sea = Connection.Airport("Seattle-Tacoma Intl Airport", connections = [dtw, lax]);
    WriteLine(lax);
    WriteLine(dtw);
    WriteLine(sea);
    }
}

Execution Result:

Airport: Name = Los Angeles Intl Airport; Connections = [no connection]
Airport: Name = Detroit Metro Wayne County; Connections = [no connection]
Airport: Name = Seattle-Tacoma Intl Airport; Connections = [Airport: Name = Detroit Metro Wayne County; Connections = [no connection], Airport: Name = Los Angeles Intl Airport; Connections = [no connection]]