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This seems like a likewise elegant solution. However, it's not immediately obvious to me how to make this work with a static type discipline. Are there language

This seems like a likewise elegant solution. However, it's not immediately obvious to me how to make this work with a static type discipline. Are there languages that do this? It seems like part of the benefits of the approaches described in the blog post is that the type system will catch incomplete extensions to the existing data or methods.

beagle3 12y ago
Nim Lang (previously Nimrod) can do that, if I understand correctly.
yummyfajitas 12y ago
In Scala, for algebraic data types like expressions and addition, you'd just use pattern matching. That would encompass the example fully. Scala has an "external" dispatch mechanism as well, basically a way to create new typed methods, namely pimping: implicit class FooWrapper(foo: Foo) extends AnyVal { def newMethod: Int = ... } val x: Foo = new Foo() x.newMethod These are all checked at compile time. Note that the example given above is actually not multiple dispatch, but merely adding methods to a type. It differs from function overloading (a Java/C++) feature only syntactically. Multiple dispatch would be dispatch on multiple type arguments, not simply one (which Julia has, but Scala does not).
- seanmcdirmid 12y ago
  As does C# with extension methods. It is especially useful when you have a generic class: class Foo<X> { ... } static class Foos { static void DoFooInt(this Foo<int> self) { .... } } new Foo<int>().DoFooInt(); I built a whole pimped library called "Bling" for C#/WPF to lift values into signal form around this technique. http://bling.codeplex.com http://bling.codeplex.com Unfortunately, operators can't be externally extended in C#, so there is still a lot of wrapper creation, but extension methods can be used for that; e.g. Signal<int> a = ..., b = ...; var c = a.Bl() + b.Bl(); Bl is an extension method for signal ints that returns a wrapper around the argument that allows for access to the + method. Bl is overloaded for a variety of types to provide access to those wrappers.

beagle3 12y ago

Nim Lang (previously Nimrod) can do that, if I understand correctly.

yummyfajitas 12y ago

In Scala, for algebraic data types like expressions and addition, you'd just use pattern matching. That would encompass the example fully. Scala has an "external" dispatch mechanism as well, basically a way to create new typed methods, namely pimping: implicit class FooWrapper(foo: Foo) extends AnyVal { def newMethod: Int = ... } val x: Foo = new Foo() x.newMethod These are all checked at compile time. Note that the example given above is actually not multiple dispatch, but merely adding methods to a type. It differs from function overloading (a Java/C++) feature only syntactically. Multiple dispatch would be dispatch on multiple type arguments, not simply one (which Julia has, but Scala does not).

seanmcdirmid 12y ago
As does C# with extension methods. It is especially useful when you have a generic class: class Foo<X> { ... } static class Foos { static void DoFooInt(this Foo<int> self) { .... } } new Foo<int>().DoFooInt(); I built a whole pimped library called "Bling" for C#/WPF to lift values into signal form around this technique. http://bling.codeplex.com http://bling.codeplex.com Unfortunately, operators can't be externally extended in C#, so there is still a lot of wrapper creation, but extension methods can be used for that; e.g. Signal<int> a = ..., b = ...; var c = a.Bl() + b.Bl(); Bl is an extension method for signal ints that returns a wrapper around the argument that allows for access to the + method. Bl is overloaded for a variety of types to provide access to those wrappers.