# Saturday, November 08, 2008

Correctly implementing structural equality involves a lot of code. My macro implements this for you.

Watch the Screencast

Before

using System;
using System.Console;
using Nemerle.Utility;
 
module Program
{
    [Record]
    public class Location
    {
        public Latitude : double;
        public Longitude : double;
 
        public override Equals(other : object) : bool
        {
            match (other)
            {
                | null => false
                | l is Location => l.Latitude == Latitude && l.Longitude == Longitude
                | _ => false;
            }
        }
 
        public override GetHashCode() : int
        {
            Latitude.GetHashCode() ^ Longitude.GetHashCode()
        }
 
        public static @==(l1 : Location, l2 : Location) : bool
        {
            def l1IsNull = object.ReferenceEquals(l1, null);
            def l2IsNull = object.ReferenceEquals(l2, null);
            match (l1IsNull, l2IsNull)
            {
                | (true, true) => true
                | (false, false) => l1.Equals(l2)
                | _ => false
            }
        }
 
        public static @!=(l1 : Location, l2 : Location) : bool
        {
            !(l1 == l2)
        }
    }
 
    module Program
    {
        Main() : void
        {
            def l1 = Location(30, 70);
            def l2 = Location(30, 70);
            def l3 = Location(40, 90);
 
            WriteLine("l1.Equals(l2) -> {0}", l1.Equals(l2));
            WriteLine("l1 == l2 -> {0}", l1 == l2);
            WriteLine("l1 != l2 -> {0}", l1 != l2);
            WriteLine("l1.GetHashCode() == l2.GetHashCode() -> {0}", l1.GetHashCode() == l2.GetHashCode());
            WriteLine("l1 != l3 -> {0}", l1 != l3);
 
            _ = ReadLine();
        }
    }
}

After

using System;
using System.Console;
using Nemerle.Utility;
using SampleMacros;
 
module Program
{
    [Record]
    [ImplementEquality(Latitude, Longitude)]
    public class Location
    {
        public Latitude : double;
        public Longitude : double;
    }
 
    module Program
    {
        Main() : void
        {
            def l1 = Location(30, 70);
            def l2 = Location(30, 70);
            def l3 = Location(40, 90);
 
            WriteLine("l1.Equals(l2) -> {0}", l1.Equals(l2));
            WriteLine("l1 == l2 -> {0}", l1 == l2);
            WriteLine("l1 != l2 -> {0}", l1 != l2);
            WriteLine("l1.GetHashCode() == l2.GetHashCode() -> {0}", l1.GetHashCode() == l2.GetHashCode());
            WriteLine("l1 != l3 -> {0}", l1 != l3);
 
            _ = ReadLine();
        }
    }
}

ImplementEquality.n

using Nemerle;
using Nemerle.Compiler;
using Nemerle.Compiler.Parsetree;
using Nemerle.Macros;
 
namespace SampleMacros
{
    [MacroUsage(MacroPhase.BeforeInheritance, MacroTargets.Class)] 
    public macro ImplementEquality(typeBuilder : TypeBuilder, params members : list[PExpr]) 
    { 
        ImplementEqualityModule.AddEqualsMethod(typeBuilder, members); 
        ImplementEqualityModule.AddEqualityOperator(typeBuilder); 
        ImplementEqualityModule.AddInequalityOperator(typeBuilder); 
    } 
 
 
    module ImplementEqualityModule 
    { 
        public AddEqualsMethod(typeBuilder : TypeBuilder, members : list[PExpr]) : void 
        { 
            def other = Macros.NewSymbol(); 
            def comparisons = members.Map(m => { 
                def s = Splicable.Name(Name(m.ToString())); 
                <[ (this.$s).Equals($(other : name).$s) ]> 
            }); 
 
 
            def b = comparisons.Tail.FoldLeft(comparisons.Head, (c, acc) => <[ $acc && $c ]>); 
            typeBuilder.Define(<[ decl: 
                public override Equals(obj : object) : bool 
                { 
                    match (obj) { 
                        | null => false 
                        | $(other : name) is $(typeBuilder.ParsedTypeName) => $b 
                        | _ => false 
                    } 
                } 
            ]>); 
 
 
            def hashCodes = members.Map(m => { def s = Splicable.Name(Name(m.ToString())); <[ this.$s.GetHashCode() ]> }); 
            def hashCode = hashCodes.Tail.FoldLeft(hashCodes.Head, (c, acc) => <[ $acc ^ $c ]>); 
            typeBuilder.Define(<[ decl: 
                public override GetHashCode() : int 
                { 
                    $hashCode 
                } 
            ]>); 
        } 
 
 
        public AddEqualityOperator(typeBuilder : TypeBuilder) : void 
        { 
            typeBuilder.Define(CreateEqualityOperator(typeBuilder.ParsedTypeName, false)); 
        } 
 
 
        public AddInequalityOperator(typeBuilder : TypeBuilder) : void 
        { 
            typeBuilder.Define(CreateEqualityOperator(typeBuilder.ParsedTypeName, true)); 
        } 
 
 
        CreateEqualityOperator(typeRef : PExpr, invert : bool) : ClassMember.Function 
        { 
            def op = Splicable.Name(Name(if (invert) "!=" else "==")); 
 
 
            <[ decl: 
                public static $op(p1 : $(typeRef), p2 : $(typeRef)) : bool 
                { 
                    def p1Null = object.ReferenceEquals(null, p1); 
                    def p2Null = object.ReferenceEquals(null, p2); 
                    match (p1Null, p2Null) { 
                        | (true, true) => true 
                        | (false, false) => $(if (invert) <[false == p1.Equals(p2)]> else <[p1.Equals(p2)]> ) 
                        | _ => false 
                    } 
                } 
            ]> 
        } 
    } 
 
 
 
}
Saturday, November 08, 2008 5:18:15 PM (GMT Standard Time, UTC+00:00)  #    Disclaimer  |  Comments [3]  | 

InheritConstructors is a handy macro when you need to simply pass all arguments to a base constructor.

Watch the Screencast 

Before

using System;

 

namespace MacrosDemo

{

    public class MyBaseClass

    {

        public this(name : string, foo : int, bar : bool)

        {

            _name = name;

            _foo = foo;

            _bar = bar;

        }

 

        _name : string;

        _foo : int;

        _bar : bool;

 

        public virtual Test() : string

        {

            "Hello from MyBaseClass"

        }

    }

 

    public class MySubClass : MyBaseClass

    {

        public this(name : string, foo : int, bar : bool)

        {

            base(name, foo, bar)

        }

 

        public override Test() : string

        {

            "Hello from MySubClass"

        }

    }

 

    module Program

    {

        Main() : void

        {

        }

    }

}

After

using System;

using Nemerle;

 

namespace MacrosDemo

{

    public class MyBaseClass

    {

        public this(name : string, foo : int, bar : bool)

        {

            _name = name;

            _foo = foo;

            _bar = bar;

        }

 

        _name : string;

        _foo : int;

        _bar : bool;

 

        public virtual Test() : string

        {

            "Hello from MyBaseClass"

        }

    }

 

    [InheritConstructors]

    public class MySubClass : MyBaseClass

    {

        public override Test() : string

        {

            "Hello from MySubClass"

        }

    }

 

    module Program

    {

        Main() : void

        {

        }

    }

}

Saturday, November 08, 2008 5:13:02 PM (GMT Standard Time, UTC+00:00)  #    Disclaimer  |  Comments [0]  | 

The [Record] macro is applied to classes and makes it very easy to create simple data-transfer objects.

Watch the Screencast

Before

using System;

 

namespace MacrosDemo

{

    public class CustomerDto

    {

        public Id : int;

        public FirstName : string;

        public LastName : string;

        public IsPrefered : bool;

 

        public this(id : int, firstName : string, lastName : string, isPrefered : bool)

        {

            Id = id;

            FirstName = firstName;

            LastName = lastName;

            IsPrefered = isPrefered;

        }

    }

 

    module Program

    {

        Main() : void

        {

            def dto = CustomerDto(1, "John", "Smith", true);

        }

    }

}

 

After

using System;

using Nemerle.Utility;

 

namespace MacrosDemo

{

    [Record]

    public class CustomerDto

    {

        public Id : int;

        public FirstName : string;

        public LastName : string;

        public IsPrefered : bool;

    }

 

    module Program

    {

        Main() : void

        {

            def dto = CustomerDto(1, "John", "Smith", true);

        }

    }

}

 

Saturday, November 08, 2008 5:04:29 PM (GMT Standard Time, UTC+00:00)  #    Disclaimer  |  Comments [0]  | 
# Sunday, July 13, 2008

Sending data from a resource to a view in a strongly-typed, but syntactically lightweight manner is not possible with C# or VB.NET.

So check out this screencast of the new "render" macro in NRest!

In a nutshell, my resource looks like:

[Resource("")]
public class RootResource
{
    public Get() : void
    {
        def test = 42;
        render (Foo = "Hello", Bar = "World", test);
    }
}

My VB.NET view looks like:

Public Class RootPage
    Inherits Page(Of RootPageContent)

    Public Overrides Function GetHtml() As XElement
        Return _
        <html>
            <body><%= Content.Foo %>, <%= Content.Bar %></body>
        </html>
    End Function
End Class

The RootPageContent DTO class is generated at compile time by the render macro. Everything is strongly-typed.

.net | dsl | macro | nemerle | nrest | REST | web
Sunday, July 13, 2008 3:27:17 PM (GMT Daylight Time, UTC+01:00)  #    Disclaimer  |  Comments [0]  | 
# Wednesday, July 02, 2008

This is a very quick video showing the work I've been doing with Nemerle, ASP.NET routing and VB 9 XML literals.
I'm trying to find the most efficient way to create RESTful web applications. I'm willing to use all the tools in the box and even make my own to achieve this.

.net | nemerle | REST | screencast | vb.net
Wednesday, July 02, 2008 11:19:24 AM (GMT Daylight Time, UTC+01:00)  #    Disclaimer  |  Comments [1]  |