Functional programming is the new hotness these days. It's also the old hotness. It's just pretty hot, really. Everyone wants to have a more functional codebase, and that's a good thing. Less side-effecty, easier to hold in your head, etc.; the benefits of FP have been thoroughly espoused elsewhere. I just have a couple of things to add about learning functional programming, especially if you're coming from another paradigm or a mixed-paradigm language (like JS).
You (Probably) Don't Need To Learn Another Language
Languages like Haskell are really neat. They'll change the way you think about writing code. But you don't need to learn a classically functional language to learn functional programming.
module Main where import System.Environment main :: IO () main = do args <- getArgs putStrLn ("Hello " ++ args !! 0)
If a block of code like that looks pretty foreign, that's okay. You can program
functionally in whatever language is most familiar to you. Probably. If you're
a C# dev or Rubyist or something, maybe you should look into something a little
less strictly OO, but if you already write JS (for example), you don't need to
go learn about abstract algebra and what stuff like
Foo :: [Bar] -> Baz Quux
means. Which leads into thought number two:
A Better Type System Doesn't Make A Language Functional
Yeah, languages like Idris and Haskell and other super mathy things are great
for functional programming, but you don't need super complex type systems to
program functionally. They're just, y'know, pretty nice. Look at
Racket, for example. You can have static typing
#lang typed/racket) but you don't have to. Similarly, you can program
functionally just fine in plain old JS, and you can write super imperative code
in TypeScript. My point is, type systems don't make a language more functional,
they make a language have a different type system.
Lots Of Languages Have A REPL
LISP people like to talk about their REPL a lot. Same with Haskell folks,
they'll tell you to go experient in GHCI. That's great, it really is. The REPL,
for any given language, should be one of the primary tools you use to figure
things out. But most languages have one. If you do Python, you're probably
familiar with it. Same with Ruby (irb or pry). Node's REPL, while a little
limited compared to GHCI, is still pretty fantastic. Racket's is very basic, but
(require xrepl) it ends up being very pleasant. Having a decent REPL
isn't a functional language feature, it's just a language ecosystem feature.
Scheme Is Really Nice
If You're Brand New To FP
Check out these links.