When comparing Vala vs Pascal, the Slant community recommends Pascal for most people. In the question“What are the best systems programming languages?” Pascal is ranked 10th while Vala is ranked 17th. The most important reason people chose Pascal is:
Because of the verbosity and easy syntax, Pascal language is relatively easier to be learned and understood, even for someone who has no programming knowledge. It's said that Pascal code —if written well— is like reading pseudo code.
Specs
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Pros
Pro Rich GTK Support
Vala developed by Gnome Foundation.
Pro Fast
Underneath there is C. It makes some stuff easier to write than it would be with plain C code.
Pro Easy Syntax
Vala is syntactically similar to C# and includes several features such as: anonymous functions, signals, properties, generics, assisted memory management, exception handling, type inference, and foreach statements
Pro Good documentation
There is Valadoc and most of the libraries have Devhelp packages.
Pro C compatible API (and ABI)
C programs can use libraries written in Vala, and vice versa.
Pro Well-integrated with C language
Vala itself is compiled to C, therefore it can use the vast ecosystem of C language, with least effort.
Pro Stable ABI
You can write a library with ABI stability.
Pro A general purpose language
Vala is compiled to C and only requires GLib - or even nothing (posix profile)
Pro Understanding of basics
Because of the verbosity and easy syntax, Pascal language is relatively easier to be learned and understood, even for someone who has no programming knowledge. It's said that Pascal code —if written well— is like reading pseudo code.
Pro Easy
Pascal / Object pascal was used in schools during the 2000's to teach kids the basics of object oriented programming.
Pro Clear syntax
Pascal's syntax is clear and concise, for example:
procedure test();
begin
DoSomething();
end;
Pro Enforces good programming practice
Numerous strong compile time checks with optional runtime checks ensure one doesn't do stupid things and even when one does (because the compiler can't prove it at compile time), the binary will check and report it at runtime.
Correct modular programming implementation with proper namespacing, no file inclusion hack.
Pro Cross platform
Pascal development tools are available almost on every available platform, especially using Free Pascal. Pascal language is available on desktop like Mac, BSD, Linux, Windows, Solaris, etc.; on mobile like iOS, Android, etc.; also on managed environments like Java Virtual Machine (JVM) and .Net/Mono framework . There are even some Pascal to JavaScript transpilers such as Smart Pascal, so you can write client side web app using Pascal as well, if you really want to.
Pro Tons of academic reading
Being known as the programming language for education, especially in the 90's, there many academic reading and tutorials available on the internet.
Pro Fast compilation
The compiler is fast, really fast. Compared to C/C++, the delphi compiler is designed to compile a decent sized desktop application in seconds rather than minutes.
Pro Flexible
Using the Free Pascal Compiler (the main Pascal distribution) you can code in a language that can be procedural and imperative now, but it can became object-oriented simply adding a directive at the start of the source
Pro Easy GUI creation
Visual Basic may have predated Delphi but Delphi was the ground breaking visual designer which set the standards expected today by most GUI developers. Its rich component set was well designed, structured and extensible, it even has the ability to display live data from the attached database in its data controls.
Pro Assembler Code and DLL/SO creation
You can put Assembler code in Intel or AT&T formats, to achieve great results of speed and accuracy. It is possible to create Dynamic Link Libraries or their equivalent in Unix-like systems so it's relatively easy to use and powerful.
Pro Rich existing libraries
Both shipped with implementations and spread all over the web. Both natively written or bindings to libraries written in other languages. Typically to build non-trivial applications there's no need to surf the web as many things are implemented already. Streaming, output templating, socket & networking, web, database, image manipulation, high performance graphics, (de)compression, (de|en)cryption, regex, unit testing, json manipulation, google API, indexing, multithreading, external process management, the list just goes on and on!
Pro Still active
From the early roots of Pascal, Delphi has been developed and is still actively supported. It is used in many desktop applications today, and even supports multi platform coding.
Pro Suitably close to modern languages, without the pitfalls
It was developed as a teaching language and it shows. No syntax pitfalls and gently encourages good style.
Pro Extensive third party libraries
There are large collections of third party components, many free which enable developers to add wide ranging and complex functionality to their code with ease
Pro Component based (reusability, decoupled, rich design architecture)
Pro Reliable language and code base
Most code from the Turbo Pascal days in the 80s still compiles, yet the language has since been adapted and extended with modern concepts, introducing OOP and interfaces, exception handling, native Unicode support, anonymous methods, generics, ARC and more.
Pro Available on a ridiculous number of platforms
FreePascal is available on/for Intel x86 (including 8086), AMD64/x86-64, PowerPC, PowerPC64, SPARC, ARM, AArch64, MIPS and the JVM. Supported operating systems include Linux, FreeBSD, Haiku, Mac OS X/iOS/iPhoneSimulator/Darwin, DOS (16 and 32 bit), Win32, Win64, WinCE, OS/2, MorphOS, Nintendo GBA, Nintendo DS, Nintendo Wii, Android, AIX and AROS.
Pro Language depth
Object Pascal is being used to write custom kernels (Ultibo) and operating-systems for various ARM boards. So the way you work with the code scales from low-level to pure OOP high-level. Object Pascal has the same level of depth that you find in C/C++ but with added productivity.
Pro Incredible GUI design tools
Lazarus and Delphi are both incredible GUI design tools, making rapid development a reality.
Making changes to a GUI doesn't mean switching tools or waiting for things to load, it's right there as part of your core tools.
Pro Dynamic evolution of language
Object Pascal language still evolving and being updated by Delphi (Embarcadero) and Free Pascal team (Lazarus).
Pro Well balanced for desktop development
For desktop development, Delphi is productive, the code is easy to understand, compilation speed is blazing, and it produces well performing applications that are easy to deploy. The perfect balance between C# and C++.
Pro Fast execution
The compiler generates fast and optimized code. No stop-the-universe garbage collection.
Pro Automatic memory management
The new Delphi compilers are powered by Automatic Reference Counting to ease development.
Pro Excellent database development
Cons
Con Very few resources allocated to the language
Only a single person is working on Vala full time. Gnome Foundation isn't allocating sufficient resources to properly maintain Vala.
Con A very naïve approach to the real problem
Vala just adds more complexity to the game. No real benefits in using a 'programming language emulator' for UI code, you may think it adds to productivity but it's just a way to make the problem last longer, reinventing the wheel everytime and worse.
Con Very limited adoption
Vala isn't used in areas other than GTK development, and no major business has adopted the language.
Con Not a general purpose language
Can't use Vala in multiple software development areas.
Con Very limited tooling
Though using Gnome Builder, you can debug it easily.
Con Heavy reliance on GObject
Heavy reliance on GObject types, although Vala can be used without GObject. (posix profile)
Con Not well documented
It already has tons of documentation, even a book about Vala.https://leanpub.com/vala https://wiki.gnome.org/Projects/Vala/Documentation
Con No stable version
No stable version of Vala released for over a decade so far. Means that Vala isn't production ready.
Con Niche language
Most use of this language will be found in jobs supporting legacy code. It will be hard to find things to do with this language outside of that niche.
Con No up-to-date version of language standards
In 1983, and update in 1990, the language was standardized with two standards: ISO/IEC 7185:1990 Pascal and ISO/IEC 10206:1990 Extended Pascal. However, Object Pascal extensions to the language have no official standards but in 1993, a draft proposal for object oriented Pascal standard was re; for review purposes only. There are no standards for modern features and enhancements, thus various Pascal dialects like Delphi or HP Pascal has their own enhancements and features.
Con Effectively obsolete
While this may have been an ok choice 25 years ago, it no longer is. Consider Python, Go or Clojure.
Con Unnecessary heavy syntax
Begin.. end. Pascal would have been great with curly braces.. but then again, that's what C is for. It's an academic language which was used in the past, but not much anymore today.