3 ms·

local syntax transformations This is the key concept, and I disagree with you that this is all Xtend is. Its why I think you are wrong. Specifically, the Xtend

by buff-a 15y ago

local syntax transformations This is the key concept, and I disagree with you that this is all Xtend is. Its why I think you are wrong. Specifically, the Xtend transformation is adding information to the java code it generates that it must infer from the Xtend source code. It is precisely not a local syntax transformation. I think you are assuming that because they make it look easy, that all it is is another macro language with, as you say, local syntax transformations.

bdj 15y ago
You misunderstand what a local syntax transformation is. A syntax transformation is just a function that takes syntax as input and returns syntax as output. The function can be arbitrarily complex, even "inferring" things from the input syntax. The key point is whether the transform is local or global. An example of a global transform is turning a program into continuation-passing style because it must change every function definition and function call in the program. The transforms that Xtend is doing appear to be local. Converting closures to anonymous inner classes is a local transformation. Their "type inference" isn't real whole-program type inference, it just saves keystrokes within certain expressions. The fact that they can show you the underlying Java code that each new feature turns into indicates that the transforms are local. Also, these types of transformations really are trivial in languages with full-featured macro systems (like most LISP dialects).
- buff-a 15y ago
  The referenced paper is way over my head, so I'll just say where I'm having difficulty and perhaps you can help me out. Java doesn't have closures. Xtend does. Closures seem to me to satisfy the paper's definition of providing greater expressibility. Certainly, I've done a lot of C# and Java, and having closures in C# has greatly influenced how I write code. And yet closures appear to be what you claim is a local syntax transform, and therefor can not add any expressibility to the language. I am confused. Update: I didnt downvote you btw.
  - skrebbel 15y ago
    Java's anonymous inner classes basically work like closures, except that they require that you mark some variables as final and that you have to write a lot of boilerplate. My underbelly feeling is that xtend's closures merely compile to those. Often, such closures are enough. E.g. with Google Guava's predicates and filter/map methods, you can do with Java (guava + anonymous inner classes) what LINQ enables in C# (System.Linq + lambda expressions). The Java version has a lot more line noise than the C# version, however, which is what Xtend fixes. I love it.
    - buff-a 15y ago
      And C++ classes merely compile to C methods with mangled names that also take a pointer to a C struct, the first member of which is a pointer to an array of such functions, and whose remaining members are the fields. If you (or GP) are going to argue that C++ is no more productive than C simply because cfront turns C++ into C, then I think theory has gotten in the way of reality.
      - skrebbel 15y ago
        Eh. I was arguing the direct opposite. I have the feeling that you're just looking to pick a fight.
      - scott_s 15y ago
        I think the key difference is if the language feature automates a kind of abstraction that was manual in the other language. For example, one can write object-oriented programs in C, but you have to do it all yourself. And C++ programs can, as you pointed out, be translated to equivalent C programs. But classes and objects in C++ are language level abstractions that don't exist in C. In that regard, I agree with you: if you want to do OO programming, one can be more productive in C++ than C. I have read much detail about Extend, but to me, the key question becomes: does it have language level abstractions that Java does not? I think closures and anonymous functions qualify, but I don't know if they're enough to make that much of a difference. But what I've seen of Extend, with the exception of closures and anonymous functions, it doesn't actually have any new abstractions. It just cleans up the syntax.

by buff-a 15y ago

bdj 15y ago

You misunderstand what a local syntax transformation is. A syntax transformation is just a function that takes syntax as input and returns syntax as output. The function can be arbitrarily complex, even "inferring" things from the input syntax. The key point is whether the transform is local or global. An example of a global transform is turning a program into continuation-passing style because it must change every function definition and function call in the program. The transforms that Xtend is doing appear to be local. Converting closures to anonymous inner classes is a local transformation. Their "type inference" isn't real whole-program type inference, it just saves keystrokes within certain expressions. The fact that they can show you the underlying Java code that each new feature turns into indicates that the transforms are local. Also, these types of transformations really are trivial in languages with full-featured macro systems (like most LISP dialects).

buff-a 15y ago
The referenced paper is way over my head, so I'll just say where I'm having difficulty and perhaps you can help me out. Java doesn't have closures. Xtend does. Closures seem to me to satisfy the paper's definition of providing greater expressibility. Certainly, I've done a lot of C# and Java, and having closures in C# has greatly influenced how I write code. And yet closures appear to be what you claim is a local syntax transform, and therefor can not add any expressibility to the language. I am confused. Update: I didnt downvote you btw.
- skrebbel 15y ago
  Java's anonymous inner classes basically work like closures, except that they require that you mark some variables as final and that you have to write a lot of boilerplate. My underbelly feeling is that xtend's closures merely compile to those. Often, such closures are enough. E.g. with Google Guava's predicates and filter/map methods, you can do with Java (guava + anonymous inner classes) what LINQ enables in C# (System.Linq + lambda expressions). The Java version has a lot more line noise than the C# version, however, which is what Xtend fixes. I love it.
  - buff-a 15y ago
    And C++ classes merely compile to C methods with mangled names that also take a pointer to a C struct, the first member of which is a pointer to an array of such functions, and whose remaining members are the fields. If you (or GP) are going to argue that C++ is no more productive than C simply because cfront turns C++ into C, then I think theory has gotten in the way of reality.
    - skrebbel 15y ago
      Eh. I was arguing the direct opposite. I have the feeling that you're just looking to pick a fight.
    - scott_s 15y ago
      I think the key difference is if the language feature automates a kind of abstraction that was manual in the other language. For example, one can write object-oriented programs in C, but you have to do it all yourself. And C++ programs can, as you pointed out, be translated to equivalent C programs. But classes and objects in C++ are language level abstractions that don't exist in C. In that regard, I agree with you: if you want to do OO programming, one can be more productive in C++ than C. I have read much detail about Extend, but to me, the key question becomes: does it have language level abstractions that Java does not? I think closures and anonymous functions qualify, but I don't know if they're enough to make that much of a difference. But what I've seen of Extend, with the exception of closures and anonymous functions, it doesn't actually have any new abstractions. It just cleans up the syntax.