Free book
Professor Frisby’s Mostly Adequate Guide to Functional Programming (javascript langauge -> some hate , some love 
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LambdaCast is a podcast about functional programming for working developers. Our focus is to describe concepts using clear everyday language without watering anything down. If you’ve ever been curious about FP but were turned off by the jargon or unfamiliar concepts, this is the place to be.
IMO functional programming (like haskell, ocaml, elixir, etc) is much easier than OOP. Functions belong to modules and not objects, and there is no funny business with inheritance. Elixir doesn’t protect you from mutable state, though. Just look at GenServers, Agents and the Process dictionary (probably the “worst” of the bunch - it allows you to qrite Python in elixir if you want to 
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For people want to go all hardcore-no-side-effects, the Haskell is the way to go. It’s quite hard to write anything in Haskell, though 
