When comparing APL vs Ceylon, the Slant community recommends Ceylon for most people. In the question“What is the best programming language to learn first?” Ceylon is ranked 35th while APL is ranked 54th. The most important reason people chose Ceylon is:
The compiler prevents you from using a potentially null variable, unless you check it is not null. Ie. it forces you to check a potentially null value before using it. The type system is strict, but flexible, allowing union and intersection of types, covariant and contravariant types, reified types, etc. Type inference and union types allows a dynamic programming style, close of JS spirit.
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No complicated loop processing to apply a function to a array of arrays. Functions are defined in a way that they will typically operate the same way on any number of array dimensions. This, along with the clear syntax, leads to very compact code that can be comprehended in a single line, rather than spread out over many pages.
Pro Clear syntax
There is no operator precedence to memorize, as everything is evaluated right-to-left. E.g., in APL 3*10+3 = 39. You do have to type in some otherwise unusual characters, such as ↓ and ∊, but those are easy enough to pick up -- and they have the advantage of being easily remembered once understood, as they often have some connection to common mathematical symbols.
You can seriously implement Conway's Game of Life in one line. There's a reason we do algebra with symbols instead of story problems. APL is good as a language of thought, since you can hold entire algorithms in your head at once.
Pro Strong static typing, null safe and flexible, almost dynamic type system
The compiler prevents you from using a potentially null variable, unless you check it is not null. Ie. it forces you to check a potentially null value before using it.
The type system is strict, but flexible, allowing union and intersection of types, covariant and contravariant types, reified types, etc.
Type inference and union types allows a dynamic programming style, close of JS spirit.
It brings type safety to JS, allowing to define interfaces to existing JS APIs, yet using the
dynamic keyword for flexible calls in the JS ecosystem.
Pro Excellent IDE support
Ceylon has reified generics, so it doesn't loose the type of collections at runtime. This makes autocompletion, debugging, etc. first-class. The Eclipse plugin makes it a full-fledged Ceylon IDE, and an IntelliJ IDEA plugin is in the works.
Pro Great tutorial
Gavin King, main author of the language, has a great, clear technical writing style, making understandable difficult concepts like variance or sound type system.
Pro Try it out in the browser
It has a Web IDE: http://try.ceylon-lang.org/ with impressive demos: http://try.ceylon-lang.org/?gist=bd41b47f325b6d32514a so you can try it without installing anything, and see the JS generation / interop in action.
Pro Excellent documentation
The language specification is very complete and up to date; also, the language module is very well documented.
Pro Easy to learn even if you don't have prior programming experience
Ceylon is indeed fairly easy and readable. Of course those ones who know OOP and a bit of functional programming concepts will feel almost at home right from the start.
Pro Generate HTML
HTML generation is supported right in the SDK.
Pro Same code in backend and frontend
APL symbols are only used by APL. You have to learn how to type them and how to read them. It doesn't work well with standard text editors , version control systems, search engines, or web forums. This makes it difficult for a beginner to find help.
Con Does not prepare you for most of the practical programming languages of today
While APL does have a strong use in certain areas (mostly mathematically intensive applications), it is a Domain-Specific language. That along with the fact that its syntax is not similar to C-like or other common syntax forms means that learning APL and expecting it to help you with learning other languages is like learning Calculus and expecting it to make English easier.
Con Write-only language
Maybe you can learn to read it with experience. And an interpreter. Reading APL is like reading a college math book. You might have to study a single line for fifteen minutes to understand what it's doing. And that's if you're an expert at APL. This also applies if you wrote it yourself more than a month ago. hopefully you have comments.
Con Flawless diamond
You can't extend the language itself. (J does this better.) Of course, what's built in is quite powerful.
Con Lack of physical or electronic books
We should hope Red Hat or anyone interested would take the time and write one. That would strengthen the maturity of the language, but Ceylon is rapidly developing which can make the author's efforts futile because his or hers work will become obsolete soon.
The second hindrance is, of course, popularity of the language which can't give much to the pockets of the author (however, Dart's unpopularity at start didn't prevent it to have a lot of printed material, but that's Google's child, we know).
Con Currently has large runtime
Ceylon 1.2 needs a language runtime of 1.55 MiB, and the Collection library adds another 370 KiB. That's a lot for the Web...
Now, this has to be put in perspective: if you use Ceylon to make a web application, these files will be loaded once, then cached by the browser (that's not casual browsing).
Moreover, most servers compress such resource, and the numbers become respectively 234 KiB and 54 KiB, which is more reasonable...