There is a question on programmers' stack exchange which touches the subject titled "Real world pitfalls of introducing F# into a large codebase and engineering team". I'm quoting:
1) Everyone has to learn F#, and it's not as trivial as switching from, say, Java to C#. Team members that have not learned F# will be unable to work on F# parts of the codebase.The fear is that maintaining F# code might be difficult because current employees and job applicants lack functional programming skills.
2) The pool of hireable F# programmers, as of now (Dec 2010) is non-existent. Search various software engineer resume databases for "F#", way less than 1% of resumes contain the keyword.
It seems some decision makers are still stuck at the time when C# 1.0, C++ and Java 2 were the languages of choice. Since then, a few things have happened.
Firstly, Python has become hugely popular. Although many were horrified by its use of white space to delimit blocks, it would be difficult to take seriously a programmer who claims he can't adjust to Python's syntax. Some love it, some hate it, but all can write Python code.
Why would the syntax of F# be any harder to adopt?
Secondly, C# has introduced a number of functional programming and other high-level concepts in each new version that has come out. Modern C# programmers are expected to master LINQ to objects, lambdas and yield return. The next version will introduce a specific syntax for asynchronous programming. Would you consider hiring a programmer would admits he knows nothing about these features and is unwilling to learn about them?
F#'s higher order functions, functions as first-class citizen, sequence expressions and asynchronous workflows match directly the modern features of C#. Why would these be harder to use in F# than in C#?
Dear reader, if you are a decision maker, I hope these two simple remarks dissipated your fears. You may be wondering why adopt F# when C# is evolving? You won't hear it from Microsoft, but the fact is that C# is breaking at the seams in its attempts to bring in new constructs. I won't give an exhaustive list, but here are a few examples of the limits of C#:
- Limits of iterator blocks (yield return). No such restriction in F#.
- Closures capture variables, not values. In F#, closures capture values, which is in my opinion a much saner design decision.
- Language-integrated queries are nice, but they don't sound as generic as they actually are. F#'s notion of quotation is more elegant, and makes it easier to see the applicability of LINQ beyond SQL.
- Although it's nice that C# is "stealing" async from F#, why not introduce the more general concept of custom workflows?
Now, I'm not saying you should ditch C# and replace it "en masse" by F#. C# has better tooling support, features implicit conversions and a lighter syntax for implicit interface inheritance. I don't think these features are a must-have in all situations, but they can be handy at times.
Adopting all new hyped technologies has its dangers, but if you refrain from getting on with the times because of a few dinosaurs among your developers, your business will eventually go the way of the dinosaurs.