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F# and Scala are both functional programming langugages that don't force the developer to only use immutable datatypes. They both have support for objects, can use libraries written in other languages and run on a virtual machine. Both languages seem to be based on ML.

What are the biggest differences between F# and Scala despite the fact that F# is designed for .NET and Scala for the Java platform?

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    – Maniero
    Commented Oct 5, 2010 at 22:27
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    functional programming langugages that don't force the developer to only use immutable datatypes - are there any, except maybe toy languages?
    – Ingo
    Commented Oct 6, 2011 at 10:43
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    @Ingo, if you think that ML and Ocaml don't qualify as functional programming languages because they allow mutability, maybe you should adjust your definition!
    – Frank Shearar
    Commented Jan 14, 2012 at 15:20
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    +Frank, you must have misunderstood: I mean, even Haskell has mutable data types. Hence, I'd still like to know which languages @Jonas has maybe in mind that would force one to use only immutable datatypes?
    – Ingo
    Commented Jan 14, 2012 at 16:21

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Major Differences:

  • Both Scala and F# combine OO-imperative programming and functional programming into one language. Their approach towards unification of paradigms is vastly different though. Scala tries to fuse the two paradigms into one (we call it object-functional paradigm), whereas F# provides the two paradigms side by side. For example, algebraic data types in F# are purely functional constructs with no OO'ness in them whereas ADTs in Scala are still regular classes and objects. (Note: In the process of compilation to CLR bytecode, even F# ADTs become classes and objects but they are not visible to F# programmer at the source level.)

  • F# has full Hindley-Milner style type inference. Scala has partial type inference. Support for subtyping and pure-OO-ness makes Hindley-Milner style type inference impossible for Scala.

  • Scala is much more minimalistic language than F#. Scala has a very small orthogonal set of constructs that are re-used throughout the language. F# seems to introduce new syntax for every little thing, thus becoming very syntax heavy as compared to Scala. (Scala has 40 keywords, whereas F# has 97. That should tell you something. :-)

  • F# being a Microsoft language has an excellent IDE support in the form of Visual Studio. Things are not so good on the Scala side. Eclipse plugin is still not upto the mark. Same goes for NetBeans plugin. IDEA seems to be your best bet at the moment, though it doesn't even come close to what you get with Java IDEs. (For Emacs fans, there's ENSIME. I have heard a lot of good things about this package, but I haven't tried it yet.)

  • Scala has far more powerful (and complex) type system than F#.

Other Differences:

  • F# functions are curried by default. In Scala, currying is available but not used very often.

  • Scala's syntax is a mix of that of Java, Standard ML, Haskell, Erlang and many many other languages. F# syntax is inspired by those of OCaml, C#, and Haskell.

  • Scala supports higher kinds and typeclasses. F# doesn't.

  • Scala is much more amenable to DSLs than F#.

PS: I love both Scala and F#, and hope they become predominant languages of their respective platforms in the future. :-)

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    This answer perpetuates several misconceptions. I'll enumerate each in turn. You said "algebraic data types in F# are purely functional constructs with no OO'ness in them" but algebraic datatypes in F# are just class and, in particular, they support augmentation with OO instance/static members and properties.
    – J D
    Commented Dec 27, 2010 at 13:48
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    You say "Scala tries to fuse the two paradigms into one (we call it object-functional paradigm)" but Scala lacks general tail call elimination and, consequently, any non-trivial functional code (including almost all conventional functional idioms such as continuation passing style and untying the recursive knot) are prone to stack overflows in Scala and, therefore, are practically useless.
    – J D
    Commented Dec 27, 2010 at 13:50
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    @JonHarrop: Scala doesn't treat ADTs specially. They are treated just like regular classes. Thereofre Some(2) in Scala has type Some[Int] and not Option[Int] which is undesirable IMO. F# on other other hand has a special syntax and treatment for ADTs, and can thus correctly infer type of Some 2 as int option. So F# encoding of ADTs is better than that of Scala's (IMO, of course). I did not try to imply that it's inferior, and I am sorry if it came across that way.
    – missingfaktor
    Commented Oct 6, 2011 at 10:55
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    @JonHarrop: The lack of TCO in JVM hasn't bothered many Scala developers. Trust me, it's not as big an issue as you seem to think. Most of the time, we are using higher order functions, instead of explicit recursion. And most higher order functions in Scala are implemented in terms of loops, and not recursion. So, lack of TCO becomes close to immaterial.
    – missingfaktor
    Commented Oct 6, 2011 at 10:57
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    I feel like this whole answer is a little biased towards Scala. For example Scala is much more minimalistic language than F# which seems to go against his argument/later point of a more complex type system.
    – Adam Gent
    Commented Feb 7, 2013 at 16:33
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  • F# is settled on functional aspects while scala is based on object-oriented aspects.
  • F# has better IDE support with Visual studio while Scala's eclipse plug-in is for open source IDE and comparatively slower.
  • F#, being more ML-like than Scala, has more of a minimal lambda calculus-y feel to it the way OCaml, Standard ML, and Scheme have. F# appears to be a considerably simpler language.
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    "F# appears to be a considerably simpler language." << No, it is not. It is way larger than Scala. I should write an article on this subject some time.
    – missingfaktor
    Commented Jan 15, 2012 at 5:05
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    "Scala is based on object-oriented aspects." << Wrong. Scala tries to fuse OOP AND functional programming. I personally very rarely use its object-oriented features. Most of what we do is purely functional.
    – missingfaktor
    Commented Jan 15, 2012 at 5:06
  • @missingfaktor: "It is way larger than Scala". How big are the grammars?
    – J D
    Commented Nov 4, 2013 at 20:00
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    I don't know if things have changed. Scala in IntelliJ rocks, with the plugin still open source.
    – Colliot
    Commented Oct 11, 2015 at 11:15
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this is also a good article on the topic: comparing-scala-to-fsharp

as always, best way is to try for yourself!

//dotnet fsi --> starts F# interactive
//or open vscode and a .fsx file, install ionide, and start typing
#r "nuget: FSharp.Data" //will download your package
open FSharp.Data

//and you are good to use it
let add x y = 
   x + y

let r = add 1 2

type MyJson = JsonProvider<"""{ "test" : "me" }""">

let sample = MyJson.GetSample()

let me = sample.Test // string! typed, and is "me"

The very big difference to understand when checking functional languages is understanding language families and history, and know why ML language was invented and why Milner won an ACM touring award for it.

https://courses.cs.washington.edu/courses/cse341/04wi/lectures/02-ml-intro.html

The Why is the ML type system. both F# and Scala are statically (strongly) typed languages, but the strongest differences in my view are:

  • Scala has no ML type inference, and never will, and has very sad curly braces like C languages used just for scoping.
  • F# doesnt have higher order kinds (scala/haskell pp brag a lot a about it) also for a language design choice, the F# lang directive thought wasn't really needed in 99% of cases of real day to day programming and would confuse people (which indeed it does most of times)
  • F# uses curly braces for CE (Computation expressions) giving curly braces a total new meaning and dignity, for building monadic operations in the best expressive way ever. (see task, async, query, etc..)

Why is scala more popular?

A note on package management:

  • package management in JVM(maven) and nodejs(npm) is more complicated...
  • package management in NET works like a charm and is amazing, plus nuget is part of the dotnet tooling, not an "external thing" anymore, so dependencies are part of your .fsproj or a line in your script .fsx amazing.

ML was the first lisp-like statically typed programming language, and OCAML also supported object orientation and imperative construct, giving the most pragmatic approach to functional programming languages.

This lets you write "like python or javascript" and have strong typing like any strongly typed language.

Pros of F#:

  • it's a NET6 language runs everywhere part of the NET6 platform
  • has scripting and a repl and can be used like python/nodejs/bash
  • has type providers and the |> pipe operator, making it awesome to work with collections and data
  • has computation expressions, a very beautiful and simple way to write custom "monadic operations" in F# (not an expert here)
  • F#6 supports natively Task
  • runs on aspnetcore easilly with beautiful libraries such as Giraffe/Saturn/Falco
  • looks much closer to javascript and is much more readeable than scala
  • transpiles to javascript with Fable compiler
  • is based on many years of academic research and 25+ years of OCAML as is an ocaml implementation for .NET, making it one of the best functional languages available today
  • doesnt (yet?) run on the JVM, but is both a .NET language and a node.js language
  • has automatic type generalization and everything is curriable
  • is supported on very good IDEs: VsCode, Rider, VisualStudio
  • is opensource since long time
  • influences many languages (like C# and Typescript)
  • F# Synthax is more accessible and better as an entry level language too (~python) for people which never started programming

Cons of F#

  • doesnt have curly braces for scoping (but has for CEs, no worries!)
  • doesnt have Higher order Kinds... Oh No! big drama moment? (btw has generic interfces..)
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    If the accepted answer reads as a little biased towards Scala, this is just blatantly a one-sided spiel about F# and fails to make a clear comparison. Note that the accepted answer was last updated over 8 years ago; much has changed in F# (can't speak to Scala) so an updated answer would be nice, but I don't think does a very good job of answering this question.
    – VisualMelon
    Commented Dec 24, 2021 at 16:15
  • yes i admit this is strongly biased in F# favor, but the bias is explained in the following points, so i see it as a "legit bias" :) or as a "strong opinion" , but i inderstand your point @VisualMelon
    – jkone27
    Commented Dec 26, 2021 at 12:54
  • This answer gave too much emphasis on curly braces!
    – lprakashv
    Commented Jan 3, 2022 at 8:10
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One small but important points is the license: Scala is BSD (pretty much the most permissive free software license there is), F# used to be "Microsoft Research Shared Source license agreement" but is a commercial product nowadays (according to @Lorenzo below, although I couldn't find more specific license agreements anywhere).

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    Actually, F# is now open source and Scala is now a commercial product of Martin Odersky's company Scala Solutions.
    – J D
    Commented Dec 27, 2010 at 13:59
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    @Jon Harrop: I think Scala Solutions is selling just Scala-related tools, services, training etc. The language itself still seems to be under the BSD license.
    – Joonas Pulakka
    Commented Dec 27, 2010 at 14:18
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    @Joonas: Exactly, the same is true of F#.
    – J D
    Commented Dec 27, 2010 at 15:51
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    @JonHarrop: Scala remains open source. Please do not spread misinformation.
    – missingfaktor
    Commented Jan 14, 2012 at 21:10
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    @missingfaktor: I didn't say Scala was closed source.
    – J D
    Commented Jan 14, 2012 at 22:05

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