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Red Hat's Ceylon language has some interesting improvements over Java:

  • The overall vision: learn from Java's mistakes, keep the good, ditch the bad
  • The focus on readability and ease of learning/use
  • Static Typing (find errors at compile time, not run time)
  • No “special” types, everything is an object
  • Named and Optional parameters (C# 4.0)
  • Nullable types (C# 2.0)
  • No need for explicit getter/setters until you are ready for them (C# 3.0)
  • Type inference via the "local" keyword (C# 3.0 "var")
  • Sequences (arrays) and their accompanying syntactic sugariness (C# 3.0)
  • Straight-forward implementation of higher-order functions

I don't know Scala but have heard it offers some similar advantages over Java.

How would Scala compare to Ceylon in this respect?

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Scala is functional. That's probably the biggest difference to start with –  charisis Apr 13 '11 at 7:27
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Scala recognises functions as first-class citizens, and makes extensive use of immutability, closures and pattern matching. It absolutely matches one very valid definition of "being functional" –  Kevin Wright Apr 13 '11 at 10:55
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Scala's collections are immutable per default, so are variables. I don't know your definition of "not making extensive use of immutability", but mine is different. –  Axel Gneiting Apr 13 '11 at 13:00
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For a strict language, Scala is as functional as any other, if "being functional" means "makes it easy to write programs in a functional style". If, however, "being functional" means "makes it hard to wite programs in a non-functional style", then Scala is not functional. The only thing I really miss in Scala in some kind of effect tracking system. –  Daniel C. Sobral Apr 13 '11 at 14:12
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I would compare them as follows: Scala exists, Ceylon doesn't. Ceylon today is where Scala was circa 2002. –  Seth Tisue Apr 13 '11 at 19:35

1 Answer 1

I started using Scala this year, and really like it. I've also attended a conference by Gavin King and talked with him about Ceylon. The idea is to have an enterprise-level replacement for Java. Some of the key features of Ceylon (not all of these exist yet) are:

  • It is intended to be used for large projects involving large teams; readability is very important, since in large projects you can spend more time reading other people's code than writing your own.
  • Everything is an object
  • There is operator overloading BUT it's not arbitrary. For example if you want to implement "+" in your class, it must implement the Summable interface. EDIT actually this is called operator polymorphism, not overloading...
  • Union and intersection types. This is BIG, one of my favorite features of the language and I haven't seen it in Scala or any other JVM language (actually I don't know where Gavin got it from but it's one of those things that I would like to have NOW in Java or any other language).
  • Everything is immutable by default, but of course you can have mutable objects by adding the "variable" keyword to your declarations.
  • Built-in builder pattern which creates immutable objects
  • No nulls by default. If you declare "String x" then x can never be null; if you want x to be null at some point you have to declare it as "String? x", and then every time you want to use x you have to guard it like "if (exists x) {bla} else {bla}"
  • The generics are much better than in Java, thanks to union and intersection types.
  • No method overloading (not needed, because of union and intersection types).
  • Local type inference (ONLY locally)
  • Null is type-safe
  • Java Interop (it's not there yet, but you'll be able to use Java classes from Ceylon, and you are able to use Ceylon classes from Java today)
  • A completely new module system. This will solve many (or hopefully all) of the problems that are today managed by Maven/Ivy and even OSGi, dependency-wise.
  • Interfaces that can have concrete members (similar to Scala traits, but Ceylon's interfaces can only have methods, no state).
  • Top-level functions and higher-order functions.
  • String interpolation
  • Two levels of visibility for classes/methods/properties/etc: shared and private.
  • Default values for method/function parameters
  • Singletons similar to Scala, by using "object" instead of "class"
  • Declaration-site variance and generic type constraints

EDIT some other features I missed the first time around:

  • Algebraic types
  • Its own SDK (language module with all the basic classes and functions)
  • JVM and javascript backends

Union and intersection types allow you to do stuff such as:

  • Declaring variables/parameters/return types that can accept two or more different types. You can have a method such as "print(String|Int p)" and it can receive either type, or "write(Cloneable&Serializable p)" and it can only receive types which implement both interfaces.
  • Heterogeneous collections. You can have a List to store objects of either type. Or a List to accept only types that implement both interfaces.
  • Generics are actually much better and simple because of these types. Instead of having stuff such as Java's "?-capture-of" which practically nobody understands how to use, you can just declare the types you need.
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I demonstrated how to code a union type in Scala (see last update), and it is nearly first-class. –  Shelby Moore III Mar 2 '12 at 13:05