I'm working to learn Haskell, and that's actually part of the appeal.
I don't expect to ever write Haskell in production. Oh, sure, some places do, but they're very, very few; I suspect it's pretty much impossible in any area where you expect to grow, simply because finding people who know it already is nearly impossible, and learning it is difficult, especially as your established crew learns new and more powerful abstractions; the amount of learning required to get someone up to speed gets higher and higher, which is not what you want as you expand.
But that said, as a developer even in more approachable languages, learning that cleverness has its benefits. It provides new insights into ways problems can be expressed. Most developers agree on the benefits of learning a new language; you learn a few good ideas, a few paradigms and approaches, that can carry over and affect the way you code in your day to day. Haskell, with its depth, is better still; you have a seemingly neverending set of ideas to learn and draw from. Many, yes, are too clever to see a full implementation elsewhere in production code that has many maintainers. But borrowing even part of an idea expressed in Haskell may lead to a simple, reusable, and concise solution to a problem that otherwise would be an ugly bug riddled one off solution.
Your assumptions are not very accurate at all. The job I just left we had moved to haskell precisely for growth. We had no problems hiring haskellers, or having our existing PHP devs learn haskell. The new job I took is getting tons of applications from experienced haskellers. There's tons of people who know haskell and don't get to use it at work. They are generally quite eager to fix that problem.
I meant it in good humor, but over the last 15 years, I have had the joy (and pain) of getting to ship production systems in a lot of less popular stacks including: Erlang (multiple), Eiffel, Haskell, and OCaml.
Hiring and training for these less popular stacks has been a goddamn nightmare in "win" conditions. You have the benefit of the better signal to noise ratio in resumes, absolutely. But, you pay for that in rarity, salary and job demands, which is fine as long as you go in eyes wide open and plan to have a small team (under 10).
Rapid team growth (from money injection, or simply success and need) is really, really hard when you don't have a large pool of qualified candidates to pull from... and training, I honestly can't fathom trying to train PHP developers in Haskell. If you company has done this successfully, please setup a newsletter, I would subscribe.
>But, you pay for that in rarity, salary and job demands
Quite the opposite. As I said, there are a lot of people who know haskell but don't get to use it in their job. There's tons of people applying for haskell jobs at $50-60k/year. Being able to use haskell is a big enough draw in and of itself.
>If you company has done this successfully, please setup a newsletter, I would subscribe.
There would be nothing to go in it. Haskell is not particularly difficult to learn. People can get up and running doing web development very quickly, without any significant changes to how they normally do things since you don't do much destructive updating in most web apps anyways.
I don't expect to ever write Haskell in production. Oh, sure, some places do, but they're very, very few; I suspect it's pretty much impossible in any area where you expect to grow, simply because finding people who know it already is nearly impossible, and learning it is difficult, especially as your established crew learns new and more powerful abstractions; the amount of learning required to get someone up to speed gets higher and higher, which is not what you want as you expand.
But that said, as a developer even in more approachable languages, learning that cleverness has its benefits. It provides new insights into ways problems can be expressed. Most developers agree on the benefits of learning a new language; you learn a few good ideas, a few paradigms and approaches, that can carry over and affect the way you code in your day to day. Haskell, with its depth, is better still; you have a seemingly neverending set of ideas to learn and draw from. Many, yes, are too clever to see a full implementation elsewhere in production code that has many maintainers. But borrowing even part of an idea expressed in Haskell may lead to a simple, reusable, and concise solution to a problem that otherwise would be an ugly bug riddled one off solution.