The fundamental problem is higher order types. When you define an interface in Java or C#, it has no way of referring to itself. Something like "compareTo" cann

The fundamental problem is higher order types. When you define an interface in Java or C#, it has no way of referring to itself. Something like "compareTo" cannot say "the other type must be exactly equal to this". So lets invent such a syntax (using a keyword "as") and write the Monad interface: interface Monad as m { const m<b> bind<a,b>(m<a>, Function<a,m<b>>); const m<a> return<a>(a); } If you fill in the implementing class for m (like IO or List or Maybe), you get the actual type signatures that would maybe be valid in C# or something.