If you're really happy and think things are dandy and don't really have an alternative, then no, stay away from Haskell and FP. As others have commented, you will not be able to code the same way after you have learned functional programming.
While FP doesn't solve everything, it does massively reduce the amount of code you write. Where I work, I started writing everything I owned in F#. After a while, I noticed all other new projects were being written in F#, even by people that had previously told me "we are sticking with C#". Why? Because they feel bad having to write loads more code to get the same work done.
Every time I have to work in C#, I'm constantly annoyed about how verbose even the tiniest things are, how much work there is.
Beware, PHP's syntax for lambdas is incredibly verbose (and IIRC there are some odd limits on how you can use them), so if you become "enlightened" then continue to try to apply it in PHP, you are in for a rough ride. Even C# which slightly embraces functional concepts, gets pretty nasty if you write in any sort of real FP style.
Where do you work that you can just take a decision like "I'm going to use language X" if you don't mind me asking?
How did you deal with concerns (which I assume your manager must have had) about skilling up the rest of your team, and your increasing component of the bus factor? [1]
I tried to make a case for F# for some parts of our codebase and got shot down!
While FP doesn't solve everything, it does massively reduce the amount of code you write. Where I work, I started writing everything I owned in F#. After a while, I noticed all other new projects were being written in F#, even by people that had previously told me "we are sticking with C#". Why? Because they feel bad having to write loads more code to get the same work done.
Every time I have to work in C#, I'm constantly annoyed about how verbose even the tiniest things are, how much work there is.
Beware, PHP's syntax for lambdas is incredibly verbose (and IIRC there are some odd limits on how you can use them), so if you become "enlightened" then continue to try to apply it in PHP, you are in for a rough ride. Even C# which slightly embraces functional concepts, gets pretty nasty if you write in any sort of real FP style.