When comparing F# vs Pharo, the Slant community recommends Pharo for most people. In the question“What is the best programming language to learn first?” Pharo is ranked 20th while F# is ranked 30th. The most important reason people chose Pharo is:
In Pharo everything is an object. Compiler - object, network - object, method - also an object. And objects communicate with messages. No operators, no control-flow statements. Just objects and messages. Few things to learn, but you can learn OOP well.
Specs
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Pros
Pro Concise syntax
F#'s syntax tends to be terse while remaining very readable and easy to understand without being a chore to write.
Pro Easier transition from other paradigms
Since F# is not a purely functional language, it lends itself to being more easily picked up by programmers that have experience with other paradigms.
Pro .NET Interoperability
Since F# runs on the Common Language Runtime or CLR, it has access to the entire .NET Framework, as well as libraries written in other .NET languages such as C#, VB.NET, and C++/CLI.
Pro Multiplatform, it runs on .Net Core
Forget Xamarin and Mono. F# now runs on the multiplatform .Net Core!
Pro You can run F# in the browser
Thanks to a project like Fable, you can write and run your client app in F# and run it over JavaScript. It allows you to share code between your server and client.
Pro Natively supported by Visual Studio
This is a .Net language natively supported by Visual Studio. Though it is not as tooled up as C# the support is still substantial. In particular, C# deployment scenarios can be enabled for it with small C# wrapper projects. Integration with Visual Studio provides: IntelliSense, debugging, projects an other features.
Pro Fall into the pit of success
F# directs you into a workflow where the right way is the path of least resistance.
Coming from a C# background, its restrictions might feel arbitrary at first (e.g., what do you mean my code has to be in dependency order!? Arbitrary alphabetical or bust!), but you'll soon realize that your code is cohesive, concise and consistent in a way that it never was before - and you can compile and run with confidence!
Pro F# is supported by Xamarin
Thanks to Xamarin, F# is a functional language that you can use to build for iOS, Android and Windows.
Pro Object-Oriented
In Pharo everything is an object. Compiler - object, network - object, method - also an object. And objects communicate with messages. No operators, no control-flow statements. Just objects and messages. Few things to learn, but you can learn OOP well.
Pro Easily learnt
There is good, free documentation including several books written by experts with extensive examples. There is an online MOOC. There are many tutorial videos. Supportive conferences and community. Even a professional support option if desired.
Pro Live updates
The nature of Pharo being a "live" environment allows you to perform live updates to your system without requiring to restart it. You can upgrade/modify classes while serving requests at the same time.
Pro Highly productive
Pro Seaside
The framework for developing sophisticated web applications in Smalltalk is developed in Pharo. Seaside lets you build highly interactive web applications quickly, reusably and maintainably.
Pro Remote debugging
Pro Beautiful coding patterns in your IDE
No need to search google for compact beautiful examples of how to do things, your live environment source is available and you can easily live search, see how it works and copy how the masters would do it (examples most languages still copy too).
Pro Glamorous toolkit & GTInspector
Most languages are still copying the Smalltalk tools of yesterday - GTInspector (written in Glamorous) takes live exploration of code/running objects to a new level. It's really slick, and better yet, you can easily write your own inspectors in 10 lines of code.
Pro Code can be run on rock solid GemStone environment
Pro 64 bit support as of Pharo 7
Use 32 bit or 64 bit versions of Pharo on Windows, Mac & Linux.
Pro Advanced code analysis tools
MOOSE environment provides extensive, easily leveraged and class leading tools for code analysis and improvement.
Pro Can run headless for production
Pro Really simple networking and REST with Zinc
Pro Graphics, graphing and visualisation framework - Roassal
Roassal and Mondrian provide fantastic and easily used frameworks for graphics, graphing and advanced visualisations (comparable to D3.js) but with much less code. Visualisations can be rendered into web friendly graphics (SVG, .png etc.) without additional work.
Cons
Con Has no ad-hoc polymorphism (á la Type Classes)
You have generics, you have interfaces, you have inheritance, you have a lot of things at your disposal but you don't have Type Clases. They can be emulated using some clever constructs but there's nothing like having the real thing.
Con Infested with OOP
Still relying on .NET OOP libraries.
Con Small community
But they are very friendly and supportive. Best help comes through the mailing lists so not always easily googlable. There is also a Slack community where help is nearly instantaneous.
Con Odd language
Requires a different mindset. Much harder to apply what you know from popular or conventional languages . Switching over from or between other languages is more difficult.
Con Single threaded
Pharo's VM only ever uses one CPU core. If you want to write code that uses more than one CPU core, you need to jump through hoops such as running multiple VMs and synchronising your data.